Remove `clang: false` support

Most everything in Soong is using clang (and we're getting very close
for Make as well), so remove the ability to select GCC to build a
module.

We still need to keep the internal functionality around to find libgcc.a
and other toolchain_library modules with GCC.

Test: m blueprint_tools
Change-Id: I5ef3e3836b9ad3e160669ac32aee39698c9b72c3

cc/cc.go

@@ -159,9 +159,12 @@ type ObjectLinkerProperties struct {
 
 // Properties used to compile all C or C++ modules
 type BaseProperties struct {
-	// compile module with clang instead of gcc
+	// Deprecated. true is the default, false is invalid.
 	Clang *bool `android:"arch_variant"`
 
+	// Some internals still need GCC (toolchain_library)
+	Gcc bool `blueprint:"mutated"`
+
 	// Minimum sdk version supported when compiling against the ndk
 	Sdk_version *string
 
@@ -1080,17 +1083,15 @@ func beginMutator(ctx android.BottomUpMutatorContext) {
 }
 
 func (c *Module) clang(ctx BaseModuleContext) bool {
-	clang := Bool(c.Properties.Clang)
-
-	if c.Properties.Clang == nil {
-		clang = true
+	if c.Properties.Clang != nil && *c.Properties.Clang == false {
+		ctx.PropertyErrorf("clang", "false (GCC) is no longer supported")
 	}
 
 	if !c.toolchain(ctx).ClangSupported() {
-		clang = false
+		panic("GCC is no longer supported")
 	}
 
-	return clang
+	return !c.Properties.Gcc
 }
 
 // Whether a module can link to another module, taking into

cc/toolchain_library.go

@@ -43,7 +43,7 @@ func toolchainLibraryFactory() android.Module {
 	}
 	module.compiler = toolchainLibrary
 	module.linker = toolchainLibrary
-	module.Properties.Clang = BoolPtr(false)
+	module.Properties.Gcc = true
 	module.stl = nil
 	module.sanitize = nil
 	module.installer = nil