Make dump_syms buildable under newer versions of Xcode.

src/tools/mac/dump_syms/dump_syms.xcodeproj/project.pbxproj

 // !$*UTF8*$!
 {
         archiveVersion = 1;
         classes = {
         };
         objectVersion = 45;
         objects = {
 
 /* Begin PBXAggregateTarget section */
                 B88FAFC9116BDCAD00407530 /* all_unittests */ = {
@@ skipping 1599 matching lines @@
                                         ../../../testing/gtest/include,
                                 );
                                 PRODUCT_NAME = macho_reader_unittest;
                         };
                         name = Release;
                 };
                 B8C5B5131166531B00D34F4E /* Debug */ = {
                         isa = XCBuildConfiguration;
                         buildSettings = {
                                 GCC_PREPROCESSOR_DEFINITIONS = HAVE_MACH_O_NLIST_H;
+                                GCC_VERSION = "";
                                 PRODUCT_NAME = dump_syms;
+                                SDKROOT = macosx;
                         };
                         name = Debug;
                 };
                 B8C5B5141166531B00D34F4E /* Release */ = {
                         isa = XCBuildConfiguration;
                         buildSettings = {
                                 GCC_PREPROCESSOR_DEFINITIONS = HAVE_MACH_O_NLIST_H;
+                                GCC_VERSION = "";
                                 PRODUCT_NAME = dump_syms;
+                                SDKROOT = macosx;
                         };
                         name = Release;
                 };
                 D21F97D411CBA0F200239E38 /* Debug */ = {
                         isa = XCBuildConfiguration;
                         buildSettings = {
                                 HEADER_SEARCH_PATHS = (
                                         $inherited,
                                         ../../../testing,
                                         ../../../testing/include,
@@ skipping 171 matching lines @@
                                 D21F97D411CBA0F200239E38 /* Debug */,
                                 D21F97D511CBA0F200239E38 /* Release */,
                         );
                         defaultConfigurationIsVisible = 0;
                         defaultConfigurationName = Release;
                 };
 /* End XCConfigurationList section */
         };
         rootObject = 08FB7793FE84155DC02AAC07 /* Project object */;
 }