cc: Filter out unknown clang cflags from InstructionSetFlags

-funswitch-loops is in the arm instruction set flags, but unsupported by
clang. Make removes clang unknown cflags from the instruction set flags.
This was producing a warning, causing -Werror to fail on libm.

Change-Id: Ibc69c9af04a738aa8adeb5549900e2b53ab754f0

1 files changed, 8 insertions, 0 deletions

diff --git a/cc/toolchain.go b/cc/toolchain.go
index d188845d..e17e345b 100644
--- a/cc/toolchain.go
+++ b/cc/toolchain.go
@@ -49,6 +49,7 @@ type Toolchain interface {
 	ClangCflags() string
 	ClangCppflags() string
 	ClangLdflags() string
+	ClangInstructionSetFlags(string) (string, error)
 
 	Is64Bit() bool
 }
@@ -63,6 +64,13 @@ func (toolchainBase) InstructionSetFlags(s string) (string, error) {
 	return "", nil
 }
 
+func (toolchainBase) ClangInstructionSetFlags(s string) (string, error) {
+	if s != "" {
+		return "", fmt.Errorf("instruction_set: %s is not a supported instruction set", s)
+	}
+	return "", nil
+}
+
 type toolchain64Bit struct {
 	toolchainBase
 }