Add only compiler-flag dependencies as implicit

Bug: http://b/72343691

Change https://android-review.googlesource.com/c/572758, in addition to
dependencies from the compiler flags, also marked all exported
dependencies as implicit.  This can cause lots of unnecessary
recompiles.  This change moves exported dependencies back as order-only
dependencies.

Test: 1. mma in art after changing profile_compilation_info.h triggers
         only a limited number of recompiles.
      2. verify that changes to PGO profile files trigger recompiles.

Change-Id: Icb0f4cd2b6da0add3b6e5206661e6aa7a577602f
diff --git a/cc/compiler.go b/cc/compiler.go
index 7e8e8b8..9b69114 100644
--- a/cc/compiler.go
+++ b/cc/compiler.go
@@ -160,7 +160,7 @@
 type baseCompiler struct {
 	Properties BaseCompilerProperties
 	Proto      android.ProtoProperties
-	genDeps    android.Paths
+	cFlagsDeps android.Paths
 	pathDeps   android.Paths
 	flags      builderFlags
 
@@ -548,16 +548,16 @@
 	srcs := append(android.Paths(nil), compiler.srcsBeforeGen...)
 
 	srcs, genDeps := genSources(ctx, srcs, buildFlags)
-	pathDeps = append(pathDeps, flags.CFlagsDeps...)
+	pathDeps = append(pathDeps, genDeps...)
 
 	compiler.pathDeps = pathDeps
-	compiler.genDeps = genDeps
+	compiler.cFlagsDeps = flags.CFlagsDeps
 
 	// Save src, buildFlags and context
 	compiler.srcs = srcs
 
 	// Compile files listed in c.Properties.Srcs into objects
-	objs := compileObjs(ctx, buildFlags, "", srcs, pathDeps, genDeps)
+	objs := compileObjs(ctx, buildFlags, "", srcs, pathDeps, compiler.cFlagsDeps)
 
 	if ctx.Failed() {
 		return Objects{}
@@ -568,7 +568,7 @@
 
 // Compile a list of source files into objects a specified subdirectory
 func compileObjs(ctx android.ModuleContext, flags builderFlags,
-	subdir string, srcFiles, pathDeps android.Paths, genDeps android.Paths) Objects {
+	subdir string, srcFiles, pathDeps android.Paths, cFlagsDeps android.Paths) Objects {
 
-	return TransformSourceToObj(ctx, subdir, srcFiles, flags, pathDeps, genDeps)
+	return TransformSourceToObj(ctx, subdir, srcFiles, flags, pathDeps, cFlagsDeps)
 }