Disable LTO when building with fuzzer support.

Bug: 131771163

LTO is currently broken when building with SANITIZE_TARGET=fuzzer. The
compiler bug is currently being addressed upstream (see linked bug), but
we have applied a local workaround in the build system to disable LTO
when building using the fuzzer config.

There is a bug here however. In the sanitizer mutator we explicitly
remove -flto and add -fno-lto. The sanitizer mutator runs after the LTO
mutator, so (in general) this works just fine. The problem exists when a
target specifies an explicit 'lto: { ... }' flag in their Android.bp. In
this case, the sanitizer mutator disables LTO, then the flags are parsed
from the Android.bp, re-enabling LTO.

This patch fixes this issue. If the sanitizer mutator has added the
-fsanitize=fuzzer-no-link flags, then the LTO mutator won't add the LTO
flags after this fact.

Test: Build a target with SANITIZE_TARGET=fuzzer (or a cc_fuzz target),
where there is an explitiy 'lto: { ... }' and watch it now succeed in
building.

Change-Id: I6643909417f666539c23469816926b806e204b06

cc/lto.go

@@ -80,6 +80,12 @@ func (lto *lto) useClangLld(ctx BaseModuleContext) bool {
 }
 
 func (lto *lto) flags(ctx BaseModuleContext, flags Flags) Flags {
+	// TODO(b/131771163): Disable LTO when using explicit fuzzing configurations.
+	// LTO breaks fuzzer builds.
+	if inList("-fsanitize=fuzzer-no-link", flags.CFlags) {
+		return flags
+	}
+
 	if lto.LTO() {
 		var ltoFlag string
 		if Bool(lto.Properties.Lto.Thin) {

cc/sanitize.go

@@ -464,7 +464,9 @@ func (sanitize *sanitize) flags(ctx ModuleContext, flags Flags) Flags {
 
 		// TODO(b/131771163): LTO and Fuzzer support is mutually incompatible.
 		_, flags.LdFlags = removeFromList("-flto", flags.LdFlags)
+		_, flags.CFlags = removeFromList("-flto", flags.CFlags)
 		flags.LdFlags = append(flags.LdFlags, "-fno-lto")
+		flags.CFlags = append(flags.CFlags, "-fno-lto")
 
 		// TODO(b/133876586): Experimental PM breaks sanitizer coverage.
 		_, flags.CFlags = removeFromList("-fexperimental-new-pass-manager", flags.CFlags)