cmd/link: suppress PIE whenever externally linking with a sanitizer

golang.org/issue/15443 complained that a race-enabled PIE binary crashed at
startup, but other ways of linking in tsan (or other sanitizers) such as

 #cgo CFLAGS: -fsanitize=thread
 #cgo LDFLAGS: -fsanitize=thread

have the same problem. Pass -no-pie to the host linker (if supported) if any
-fsanitizer=foo cgo LDFLAG is seen when linking.

Fixes #15887

Change-Id: Id799770f8d045f6f40fa8c463563937a5748d1a8
Reviewed-on: https://go-review.googlesource.com/23535
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/link/internal/ld/lib.go

@@ -1222,13 +1222,21 @@ func hostlink() {
 		}
 	}
 
+	sanitizers := flag_race != 0
+
+	for _, flag := range ldflag {
+		if strings.HasPrefix(flag, "-fsanitize=") {
+			sanitizers = true
+		}
+	}
+
 	argv = append(argv, ldflag...)
 
-	if flag_race != 0 {
+	if sanitizers {
 		// On a system where the toolchain creates position independent
-		// executables by default, tsan initialization can fail. So we pass
+		// executables by default, tsan/msan/asan/etc initialization can
-		// -no-pie here, but support for that flag is quite new and we test
+		// fail. So we pass -no-pie here, but support for that flag is quite
-		// for its support first.
+		// new and we test for its support first.
 		src := filepath.Join(tmpdir, "trivial.c")
 		if err := ioutil.WriteFile(src, []byte{}, 0666); err != nil {
 			Ctxt.Diag("WriteFile trivial.c failed: %v", err)