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/arm_device.go b/cc/arm_device.go
index ddda33c..a6c1911 100644
--- a/cc/arm_device.go
+++ b/cc/arm_device.go
@@ -161,8 +161,6 @@
 	pctx.SourcePathVariable("armGccRoot",
 		"prebuilts/gcc/${HostPrebuiltTag}/arm/arm-linux-androideabi-${armGccVersion}")
 
-	pctx.StaticVariable("armGccTriple", "arm-linux-androideabi")
-
 	pctx.StaticVariable("armToolchainCflags", strings.Join(armToolchainCflags, " "))
 	pctx.StaticVariable("armCflags", strings.Join(armCflags, " "))
 	pctx.StaticVariable("armLdflags", strings.Join(armLdflags, " "))
@@ -269,7 +267,7 @@
 }
 
 func (t *toolchainArm) GccTriple() string {
-	return "${armGccTriple}"
+	return "arm-linux-androideabi"
 }
 
 func (t *toolchainArm) GccVersion() string {
@@ -308,7 +306,7 @@
 }
 
 func (t *toolchainArm) ClangTriple() string {
-	return "${armGccTriple}"
+	return t.GccTriple()
 }
 
 func (t *toolchainArm) ToolchainClangCflags() string {