Build PDFium with -std=c++11 instead of g++11.

R=thakis@chromium.org

Review URL: https://codereview.chromium.org/1734593004 .
diff --git a/build/standalone.gypi b/build/standalone.gypi
index dfd5617..f00af23 100644
--- a/build/standalone.gypi
+++ b/build/standalone.gypi
@@ -182,7 +182,7 @@
       '-fvisibility=hidden',
     ],
     'cflags_cc': [
-      '-std=gnu++0x',
+      '-std=c++11',
       '-Wnon-virtual-dtor',
       '-fno-rtti',
     ],
@@ -333,7 +333,7 @@
     },
     'xcode_settings': {
       'ALWAYS_SEARCH_USER_PATHS': 'NO',
-      'CLANG_CXX_LANGUAGE_STANDARD': 'gnu++11',
+      'CLANG_CXX_LANGUAGE_STANDARD': 'c++11',
       'GCC_CW_ASM_SYNTAX': 'NO',                # No -fasm-blocks
       'GCC_DYNAMIC_NO_PIC': 'NO',               # No -mdynamic-no-pic
                                                 # (Equivalent to -fPIC)