Expose real GccVersion

In order to validate that the NDK STL paths exists, we need to know
the full path, including the Gcc version during the go execution. So
instead of returning a ninja variable reference, just return the
contents of the variable.

This also fixes a few invalid uses of armGccVersion to the proper
variable.

Change-Id: I54398ba4aa4000235b7d537a2c4efe3ecbbeec8b

cc/x86_linux_host.go

@@ -101,8 +101,12 @@ var (
 	}
 )
 
+const (
+	linuxGccVersion = "4.8"
+)
+
 func init() {
-	pctx.StaticVariable("linuxGccVersion", "4.8")
+	pctx.StaticVariable("linuxGccVersion", linuxGccVersion)
 
 	pctx.StaticVariable("linuxGccRoot",
 		"${SrcDir}/prebuilts/gcc/${HostPrebuiltTag}/host/x86_64-linux-glibc2.15-${linuxGccVersion}")
@@ -163,7 +167,7 @@ func (t *toolchainLinux) GccTriple() string {
 }
 
 func (t *toolchainLinux) GccVersion() string {
-	return "${linuxGccVersion}"
+	return linuxGccVersion
 }
 
 func (t *toolchainLinuxX86) Cflags() string {