Make unit_tests compile in Mac GN

third_party/libexif/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Linux should use system libexif
 if (!is_linux || is_chromeos) {
   # TODO(thestig): Properly support building on Linux.
   config("libexif_config") {
     include_dirs = [ "sources" ]
     if (is_clang) {
       cflags = [
         "-Wno-enum-conversion",
         "-Wno-switch",
         "-Wno-format",
 
         # libexif uses fabs(int) to cast to float.
         "-Wno-absolute-value",
       ]
     }
   }
 
-  shared_library("libexif") {
+  loadable_module("libexif") {
     sources = [
       "sources/libexif/canon/exif-mnote-data-canon.c",
       "sources/libexif/canon/mnote-canon-entry.c",
       "sources/libexif/canon/mnote-canon-tag.c",
       "sources/libexif/exif-byte-order.c",
       "sources/libexif/exif-content.c",
       "sources/libexif/exif-data.c",
       "sources/libexif/exif-entry.c",
       "sources/libexif/exif-format.c",
       "sources/libexif/exif-ifd.c",
@@ skipping 33 matching lines @@
     } else if (is_linux) {
       libs = [ "m" ]
     }
 
     configs -= [ "//build/config/compiler:chromium_code" ]
     configs += [ "//build/config/compiler:no_chromium_code" ]
 
     public_configs = [ ":libexif_config" ]
   }
 }