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/mips_device.go b/cc/config/mips_device.go
index b815fc6..eb44fd5 100644
--- a/cc/config/mips_device.go
+++ b/cc/config/mips_device.go
@@ -210,7 +210,7 @@
 	return "${config.MipsClangLdflags}"
 }
 
-func (toolchainMips) SanitizerRuntimeLibraryArch() string {
+func (toolchainMips) LibclangRuntimeLibraryArch() string {
 	return "mips"
 }