Resolve GccTriple/ClangTriple early.

When these are Ninja variable they can't be used in android.Path since
they'll be rejected as invalid paths. We don't actually need them to be
a Ninja variable, so make them plain old strings instead.

Test: Still builds.
Change-Id: I04743cebd4b2f9be5685545f2ee941df180fce14
diff --git a/cc/x86_device.go b/cc/x86_device.go
index ba2f23a..550aca0 100644
--- a/cc/x86_device.go
+++ b/cc/x86_device.go
@@ -159,8 +159,6 @@
 	pctx.SourcePathVariable("x86GccRoot",
 		"prebuilts/gcc/${HostPrebuiltTag}/x86/x86_64-linux-android-${x86GccVersion}")
 
-	pctx.StaticVariable("x86GccTriple", "x86_64-linux-android")
-
 	pctx.StaticVariable("x86ToolchainCflags", "-m32")
 	pctx.StaticVariable("x86ToolchainLdflags", "-m32")
 
@@ -198,7 +196,7 @@
 }
 
 func (t *toolchainX86) GccTriple() string {
-	return "${x86GccTriple}"
+	return "x86_64-linux-android"
 }
 
 func (t *toolchainX86) GccVersion() string {