- fix building with system gtest
- remove -std=c++11; gtest wants at least C++14

Index: cmake/utils.cmake
--- cmake/utils.cmake.orig
+++ cmake/utils.cmake
@@ -18,7 +18,7 @@ function (shaderc_use_gmock TARGET)
   target_include_directories(${TARGET} PRIVATE
     ${gmock_SOURCE_DIR}/include
     ${gtest_SOURCE_DIR}/include)
-  target_link_libraries(${TARGET} PRIVATE gmock gtest_main)
+  target_link_libraries(${TARGET} PRIVATE gmock gtest gtest_main)
 endfunction(shaderc_use_gmock)
 
 function(shaderc_default_c_compile_options TARGET)
@@ -59,7 +59,7 @@ endfunction(shaderc_default_c_compile_options)
 function(shaderc_default_compile_options TARGET)
   shaderc_default_c_compile_options(${TARGET})
   if (NOT "${MSVC}")
-    target_compile_options(${TARGET} PRIVATE -std=c++11)
+    target_compile_options(${TARGET} PRIVATE)
     if (NOT SHADERC_ENABLE_SHARED_CRT)
       if (WIN32)
         # For MinGW cross compile, statically link to the C++ runtime.