Add BuiltinsRuntimeLibrary

... and rename SanitizerRuntimeLibrary to LibclangRuntimeLibrary since
some of them are not sanitizers.

Bug: 29275768
Test: m
Change-Id: Id638adea42d22b02438fce26120aa155bea14d42
diff --git a/cc/config/x86_device.go b/cc/config/x86_device.go
index 15188cf..ffdf8ea 100644
--- a/cc/config/x86_device.go
+++ b/cc/config/x86_device.go
@@ -251,7 +251,7 @@
 	return "${config.X86YasmFlags}"
 }
 
-func (toolchainX86) SanitizerRuntimeLibraryArch() string {
+func (toolchainX86) LibclangRuntimeLibraryArch() string {
 	return "i686"
 }