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/arm_device.go b/cc/config/arm_device.go
index 4719fb7..4135179 100644
--- a/cc/config/arm_device.go
+++ b/cc/config/arm_device.go
@@ -397,7 +397,7 @@
 	}
 }
 
-func (toolchainArm) SanitizerRuntimeLibraryArch() string {
+func (toolchainArm) LibclangRuntimeLibraryArch() string {
 	return "arm"
 }