cmake: export <atomic> availability (fixes #667)

CMakeLists.txt

@@ -398,6 +398,12 @@ if (HAVE_EXECINFO_H)
   set (HAVE_STACKTRACE 1)
 endif (HAVE_EXECINFO_H)
 
+if (HAVE_CXX11_ATOMIC)
+  set (ac_cv_cxx11_atomic 1)
+else (HAVE_CXX11_ATOMIC)
+  set (ac_cv_cxx11_atomic 0)
+endif (HAVE_CXX11_ATOMIC)
+
 if (WITH_SYMBOLIZE)
   if (WIN32 OR CYGWIN)
     cmake_push_check_state (RESET)
@@ -466,7 +472,7 @@ else (WITH_THREADS AND Threads_FOUND)
   set (NO_THREADS 1)
 endif (WITH_THREADS AND Threads_FOUND)
 
-# fopen/open on Cygwin can not handle unix-type paths like /home/.... 
+# fopen/open on Cygwin can not handle unix-type paths like /home/....
 # therefore we translate TEST_SRC_DIR to windows-path.
 if (CYGWIN)
   execute_process (COMMAND cygpath.exe -m ${CMAKE_CURRENT_SOURCE_DIR}

bazel/glog.bzl

@@ -187,6 +187,7 @@ def glog_library(namespace = "google", with_gflags = 1, **kwargs):
     )
 
     common_config = {
+        "@ac_cv_cxx11_atomic@": "1",
         "@ac_cv_cxx11_nullptr_t@": "1",
         "@ac_cv_cxx_using_operator@": "1",
         "@ac_cv_have_inttypes_h@": "0",

src/glog/logging.h.in

@@ -99,7 +99,7 @@
 #include <gflags/gflags.h>
 #endif
 
-#ifdef HAVE_CXX11_ATOMIC
+#if @ac_cv_cxx11_atomic@
 #include <atomic>
 #elif defined(OS_WINDOWS)
 #include <Windows.h>