crdmg: Use __builtin_available/availability instead of -mmacosx-version-min.

We can't use @available in this file because that is only available
in Objective C.

Bug: 735328
Change-Id: I09ed1b2bcc46fceafc4bfb84800d18177fd4f4a3
Reviewed-on: https://chromium-review.googlesource.com/566956Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Jialiu Lin <jialiul@chromium.org>
Reviewed-by: Sidney San Martin <sdy@chromium.org>
Commit-Queue: Peter Collingbourne <pcc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485783}

chrome/utility/safe_browsing/mac/BUILD.gn

@@ -2,7 +2,6 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//build/config/sysroot.gni")
 import("//testing/libfuzzer/fuzzer_test.gni")
 
 source_set("mac") {
@@ -49,19 +48,6 @@ source_set("dmg_common") {
   public_configs = [ ":dmg_public_config" ]
 }
 
-config("10_10_config") {
-  cflags = [
-    "-isysroot",
-    sysroot,
-    "-mmacosx-version-min=10.10",
-  ]
-  ldflags = [
-    "-isysroot",
-    sysroot,
-    "-mmacosx-version-min=10.10",
-  ]
-}
-
 executable("crdmg") {
   sources = [
     "crdmg.cc",
@@ -72,9 +58,6 @@ executable("crdmg") {
     "//base",
     "//sandbox/mac:seatbelt",
   ]
-
-  configs -= [ "//build/config/compiler:runtime_library" ]
-  configs += [ ":10_10_config" ]
 }
 
 fuzzer_test("safe_browsing_dmg_fuzzer") {

chrome/utility/safe_browsing/mac/crdmg.cc

@@ -53,7 +53,7 @@ class SafeDMG {
   bool EnableSandbox();
 
   // Performs the actual DMG operation.
-  bool ParseDMG();
+  __attribute__((availability(macos, introduced = 10.10))) bool ParseDMG();
 
   base::File dmg_file_;
 
@@ -91,8 +91,13 @@ int SafeDMG::Main(int argc, const char* argv[]) {
   if (!EnableSandbox())
     return EXIT_FAILURE;
 
+  if (__builtin_available(macOS 10.10, *)) {
     if (!ParseDMG())
       return EXIT_FAILURE;
+  } else {
+    LOG(ERROR) << "Requires 10.10 or higher";
+    return EXIT_FAILURE;
+  }
 
   return EXIT_SUCCESS;
 }