Use ifndef or ifeq () instead of ifeq ""

ifeq with quotes is technically correct make syntax, but rarely used.
Replace it with the simpler ifndef when comparing against empty, or
with parenthesis for consistency.

Test: builds
Change-Id: Idcbe0586c4626c67d560694596b0bd9f5f93484a

core/Makefile

@@ -5,7 +5,7 @@
 LOCAL_PATH := $(BUILD_SYSTEM)
 
 # Pick a reasonable string to use to identify files.
-ifneq "" "$(filter eng.%,$(BUILD_NUMBER))"
+ifneq (,$(filter eng.%,$(BUILD_NUMBER)))
   # BUILD_NUMBER has a timestamp in it, which means that
   # it will change every time.  Pick a stable value.
   FILE_NAME_TAG := eng.$(USER)
@@ -171,7 +171,7 @@ ifeq ($(TARGET_BUILD_VARIANT),user)
   # release build number or branch.buld_number non-release builds
 
   # Dev. branches should have DISPLAY_BUILD_NUMBER set
-  ifeq "true" "$(DISPLAY_BUILD_NUMBER)"
+  ifeq (true,$(DISPLAY_BUILD_NUMBER))
     BUILD_DISPLAY_ID := $(BUILD_ID).$(BUILD_NUMBER_FROM_FILE) $(BUILD_KEYS)
   else
     BUILD_DISPLAY_ID := $(BUILD_ID) $(BUILD_KEYS)

core/cleanbuild.mk

@@ -165,7 +165,7 @@ PREVIOUS_BUILD_CONFIG :=
 PREVIOUS_BUILD_CONFIG := $(strip $(PREVIOUS_BUILD_CONFIG))
 
 ifdef PREVIOUS_BUILD_CONFIG
-  ifneq "$(current_build_config)" "$(PREVIOUS_BUILD_CONFIG)"
+  ifneq ($(current_build_config),$(PREVIOUS_BUILD_CONFIG))
     $(info *** Build configuration changed: "$(PREVIOUS_BUILD_CONFIG)" -> "$(current_build_config)")
     ifneq ($(DISABLE_AUTO_INSTALLCLEAN),true)
       force_installclean := true
@@ -272,7 +272,7 @@ installclean: dataclean
 	$(hide) rm -rf $(FILES)
 	@echo "Deleted images and staging directories."
 
-ifeq "$(force_installclean)" "true"
+ifeq ($(force_installclean),true)
   $(info *** Forcing "make installclean"...)
   $(info *** rm -rf $(dataclean_files) $(installclean_files))
   $(shell rm -rf $(dataclean_files) $(installclean_files))

core/version_defaults.mk

@@ -34,7 +34,7 @@
 # if the file exists.
 #
 INTERNAL_BUILD_ID_MAKEFILE := $(wildcard $(BUILD_SYSTEM)/build_id.mk)
-ifneq "" "$(INTERNAL_BUILD_ID_MAKEFILE)"
+ifdef INTERNAL_BUILD_ID_MAKEFILE
   include $(INTERNAL_BUILD_ID_MAKEFILE)
 endif
 
@@ -76,7 +76,7 @@ ENABLED_VERSIONS := $(call find_and_earlier,$(ALL_VERSIONS),$(TARGET_PLATFORM_VE
 $(foreach v,$(ENABLED_VERSIONS), \
   $(eval IS_AT_LEAST_$(v) := true))
 
-ifeq "" "$(PLATFORM_VERSION)"
+ifndef PLATFORM_VERSION
   # This is the canonical definition of the platform version,
   # which is the version that we reveal to the end user.
   # Update this value when the platform version changes (rather
@@ -84,7 +84,7 @@ ifeq "" "$(PLATFORM_VERSION)"
   PLATFORM_VERSION := 7.1.1
 endif
 
-ifeq "" "$(PLATFORM_SDK_VERSION)"
+ifndef PLATFORM_SDK_VERSION
   # This is the canonical definition of the SDK version, which defines
   # the set of APIs and functionality available in the platform.  It
   # is a single integer that increases monotonically as updates to
@@ -96,7 +96,7 @@ ifeq "" "$(PLATFORM_SDK_VERSION)"
   PLATFORM_SDK_VERSION := 25
 endif
 
-ifeq "" "$(PLATFORM_JACK_MIN_SDK_VERSION)"
+ifndef PLATFORM_JACK_MIN_SDK_VERSION
   # This is definition of the min SDK version given to Jack for the current
   # platform. For released version it should be the same as
   # PLATFORM_SDK_VERSION. During development, this number may be incremented
@@ -105,7 +105,7 @@ ifeq "" "$(PLATFORM_JACK_MIN_SDK_VERSION)"
   PLATFORM_JACK_MIN_SDK_VERSION := o-b1
 endif
 
-ifeq "" "$(PLATFORM_VERSION_CODENAME)"
+ifndef PLATFORM_VERSION_CODENAME
   # This is the current development code-name, if the build is not a final
   # release build.  If this is a final release build, it is simply "REL".
   PLATFORM_VERSION_CODENAME := REL
@@ -116,10 +116,10 @@ ifeq "" "$(PLATFORM_VERSION_CODENAME)"
   PLATFORM_VERSION_ALL_CODENAMES := $(PLATFORM_VERSION_CODENAME)
 endif
 
-ifeq "REL" "$(PLATFORM_VERSION_CODENAME)"
+ifeq (REL,$(PLATFORM_VERSION_CODENAME))
   PLATFORM_PREVIEW_SDK_VERSION := 0
 else
-  ifeq "" "$(PLATFORM_PREVIEW_SDK_VERSION)"
+  ifndef PLATFORM_PREVIEW_SDK_VERSION
     # This is the definition of a preview SDK version over and above the current
     # platform SDK version. Unlike the platform SDK version, a higher value
     # for preview SDK version does NOT mean that all prior preview APIs are
@@ -133,20 +133,20 @@ else
   endif
 endif
 
-ifeq "" "$(DEFAULT_APP_TARGET_SDK)"
+ifndef DEFAULT_APP_TARGET_SDK
   # This is the default minSdkVersion and targetSdkVersion to use for
   # all .apks created by the build system.  It can be overridden by explicitly
   # setting these in the .apk's AndroidManifest.xml.  It is either the code
   # name of the development build or, if this is a release build, the official
   # SDK version of this release.
-  ifeq "REL" "$(PLATFORM_VERSION_CODENAME)"
+  ifeq (REL,$(PLATFORM_VERSION_CODENAME))
     DEFAULT_APP_TARGET_SDK := $(PLATFORM_SDK_VERSION)
   else
     DEFAULT_APP_TARGET_SDK := $(PLATFORM_VERSION_CODENAME)
   endif
 endif
 
-ifeq "" "$(PLATFORM_SECURITY_PATCH)"
+ifndef PLATFORM_SECURITY_PATCH
     #  Used to indicate the security patch that has been applied to the device.
     #  It must signify that the build includes all security patches issued up through the designated Android Public Security Bulletin.
     #  It must be of the form "YYYY-MM-DD" on production devices.
@@ -155,7 +155,7 @@ ifeq "" "$(PLATFORM_SECURITY_PATCH)"
       PLATFORM_SECURITY_PATCH := 2016-11-05
 endif
 
-ifeq "" "$(PLATFORM_BASE_OS)"
+ifndef PLATFORM_BASE_OS
   # Used to indicate the base os applied to the device.
   # Can be an arbitrary string, but must be a single word.
   #
@@ -163,7 +163,7 @@ ifeq "" "$(PLATFORM_BASE_OS)"
   PLATFORM_BASE_OS :=
 endif
 
-ifeq "" "$(BUILD_ID)"
+ifndef BUILD_ID
   # Used to signify special builds.  E.g., branches and/or releases,
   # like "M5-RC7".  Can be an arbitrary string, but must be a single
   # word and a valid file name.
@@ -172,7 +172,7 @@ ifeq "" "$(BUILD_ID)"
   BUILD_ID := UNKNOWN
 endif
 
-ifeq "" "$(BUILD_DATETIME)"
+ifndef BUILD_DATETIME
   # Used to reproduce builds by setting the same time. Must be the number
   # of seconds since the Epoch.
   BUILD_DATETIME := $(shell date +%s)
@@ -184,7 +184,7 @@ else
 DATE := date -d @$(BUILD_DATETIME)
 endif
 
-ifeq "" "$(BUILD_NUMBER)"
+ifndef BUILD_NUMBER
   # BUILD_NUMBER should be set to the source control value that
   # represents the current state of the source code.  E.g., a
   # perforce changelist number or a git hash.  Can be an arbitrary string