apex: __ANDROID_APEX__ defined with no value

__ANDROID_APEX__ was defined with the name of apex module.
-D__ANDROID_APEX__=com.android.foo

But in this way, conditional compilation is not easy since comparing
macro's string value is not supported in C/C++.
(There's no usages of this value in source tree.)

In most cases, modules can check if __ANDROID_APEX__ is defined to see
if they are compiled for apex.
For modules which should behave differently according to which apex they
are included, they can check __ANDROID_APEX_<NAME>__.

Bug: 142582178
Test: m (soong tests run) && boot device && TH
Change-Id: I0f5e3e9463ccd96cbba333a8bdd648470c5c912d
diff --git a/apex/apex_test.go b/apex/apex_test.go
index ffbee86..2271645 100644
--- a/apex/apex_test.go
+++ b/apex/apex_test.go
@@ -1212,24 +1212,21 @@
 		}
 	`)
 
-	// non-APEX variant does not have __ANDROID__APEX__ defined
+	// non-APEX variant does not have __ANDROID_APEX(_NAME)__ defined
 	mylibCFlags := ctx.ModuleForTests("mylib", "android_arm64_armv8-a_core_static").Rule("cc").Args["cFlags"]
-	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX__=myapex")
-	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX__=otherapex")
+	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX__")
 	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX_MYAPEX__")
 	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX_OTHERAPEX__")
 
-	// APEX variant has __ANDROID_APEX__=<apexname> defined
+	// APEX variant has __ANDROID_APEX(_NAME)__ defined
 	mylibCFlags = ctx.ModuleForTests("mylib", "android_arm64_armv8-a_core_static_myapex").Rule("cc").Args["cFlags"]
-	ensureContains(t, mylibCFlags, "-D__ANDROID_APEX__=myapex")
-	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX__=otherapex")
+	ensureContains(t, mylibCFlags, "-D__ANDROID_APEX__")
 	ensureContains(t, mylibCFlags, "-D__ANDROID_APEX_MYAPEX__")
 	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX_OTHERAPEX__")
 
-	// APEX variant has __ANDROID_APEX__=<apexname> defined
+	// APEX variant has __ANDROID_APEX(_NAME)__ defined
 	mylibCFlags = ctx.ModuleForTests("mylib", "android_arm64_armv8-a_core_static_otherapex").Rule("cc").Args["cFlags"]
-	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX__=myapex")
-	ensureContains(t, mylibCFlags, "-D__ANDROID_APEX__=otherapex")
+	ensureContains(t, mylibCFlags, "-D__ANDROID_APEX__")
 	ensureNotContains(t, mylibCFlags, "-D__ANDROID_APEX_MYAPEX__")
 	ensureContains(t, mylibCFlags, "-D__ANDROID_APEX_OTHERAPEX__")
 }
diff --git a/cc/compiler.go b/cc/compiler.go
index 438dee7..ff68101 100644
--- a/cc/compiler.go
+++ b/cc/compiler.go
@@ -320,8 +320,7 @@
 	}
 
 	if ctx.apexName() != "" {
-		// TODO(b/142582178): remove the value for __ANDROID_APEX__
-		flags.GlobalFlags = append(flags.GlobalFlags, "-D__ANDROID_APEX__="+ctx.apexName())
+		flags.GlobalFlags = append(flags.GlobalFlags, "-D__ANDROID_APEX__")
 		flags.GlobalFlags = append(flags.GlobalFlags, "-D__ANDROID_APEX_"+makeDefineString(ctx.apexName())+"__")
 	}