Run `uname -sm` once, don't use python for HOST_OS_EXTRA

This saves 20-50ms for `lunch` (~7-10%), and double that for every build
execution.

Test: Check HOST_OS_EXTRA on Linux & Mac
Change-Id: I863200b2287c8867f40606237895b1d3ad91e1b3

core/config.mk

@@ -71,6 +71,8 @@ $(warning The build system needs unmodified output of grep.)
 $(error Please remove --color=always from your  $$GREP_OPTIONS)
 endif
 
+UNAME := $(shell uname -sm)
+
 SRC_TARGET_DIR := $(TOPDIR)build/target
 SRC_API_DIR := $(TOPDIR)prebuilts/sdk/api
 SRC_SYSTEM_API_DIR := $(TOPDIR)prebuilts/sdk/system-api

core/envsetup.mk

@@ -97,8 +97,6 @@ endif
 # compiles except for arm/mips, so the HOST is whatever we are
 # running on
 
-UNAME := $(shell uname -sm)
-
 # HOST_OS
 ifneq (,$(findstring Linux,$(UNAME)))
   HOST_OS := linux
@@ -110,7 +108,15 @@ ifneq (,$(findstring Macintosh,$(UNAME)))
   HOST_OS := darwin
 endif
 
-HOST_OS_EXTRA:=$(shell python -c "import platform; print(platform.platform())")
+HOST_OS_EXTRA := $(shell uname -rsm)
+ifeq ($(HOST_OS),linux)
+  ifneq ($(wildcard /etc/os-release),)
+    HOST_OS_EXTRA += $(shell source /etc/os-release; echo $$PRETTY_NAME)
+  endif
+else ifeq ($(HOST_OS),darwin)
+  HOST_OS_EXTRA += $(shell sw_vers -productVersion)
+endif
+HOST_OS_EXTRA := $(subst $(space),-,$(HOST_OS_EXTRA))
 
 # BUILD_OS is the real host doing the build.
 BUILD_OS := $(HOST_OS)

core/version_defaults.mk

@@ -212,7 +212,7 @@ ifndef BUILD_DATETIME
   BUILD_DATETIME := $(shell date +%s)
 endif
 
-ifneq (,$(findstring Darwin,$(shell uname -sm)))
+ifneq (,$(findstring Darwin,$(UNAME)))
 DATE := date -r $(BUILD_DATETIME)
 else
 DATE := date -d @$(BUILD_DATETIME)