Remove GCC support from Make

We need to keep support in Soong until toolchain_library no longer uses
GCC.

Test: out/build-aosp_arm64.ninja is the same before/after
Test: build_test on downstream branches
Change-Id: Ib78bcd6d5544afc3a3164f65fa72a3f08b2acf29

cc/cc.go

@@ -1089,10 +1089,6 @@ func (c *Module) clang(ctx BaseModuleContext) bool {
 		ctx.PropertyErrorf("clang", "false (GCC) is no longer supported")
 	}
 
-	if !c.toolchain(ctx).ClangSupported() {
-		panic("GCC is no longer supported")
-	}
-
 	return !c.Properties.Gcc
 }