Guard thread_local

Mac OS X 10.9 supports __thread but not C++11 thread_local.
Teach CMake to detect support for thread_local and use the proper
define guard.

Fixes #7023

cmake/ConfigureChecks.cmake

@@ -186,6 +186,16 @@ int main () {
   HAVE_STD__MAKE_UNIQUE
 )
 
+# Detect support for thread_local.
+check_cxx_source_compiles("
+int main () {
+  static thread_local int x = 3;
+  (void)x;
+}
+"
+  HAVE_CX11_THREAD_LOCAL
+)
+
 find_program(SED sed)
 
 check_cxx_source_compiles("

config_cmake.h.in

@@ -10,6 +10,9 @@
 /* Define to 1 if you have the `ctermid_r' function. */
 #cmakedefine HAVE_CTERMID_R 1
 
+/* Define to 1 if C++11 thread_local is supported. */
+#cmakedefine HAVE_CX11_THREAD_LOCAL 1
+
 /* Define to 1 if you have the `dirfd' function. */
 #cmakedefine HAVE_DIRFD 1
 

src/fallback.h

@@ -34,6 +34,18 @@ int fish_wcswidth(const wchar_t *str, size_t n);
 // otherwise it uses mkstemp followed by fcntl
 int fish_mkstemp_cloexec(char *);
 
+/// thread_local support.
+#if HAVE_CX11_THREAD_LOCAL
+# define FISH_THREAD_LOCAL thread_local
+#elif defined (__GNUC__)
+# define FISH_THREAD_LOCAL __thread
+#elif defined (_MSC_VER)
+# define FISH_THREAD_LOCAL __declspec(thread)
+#else // !C++11 && !__GNUC__ && !_MSC_VER
+# error "No known thread local storage qualifier for this platform"
+#endif
+
+
 #ifndef WCHAR_MAX
 /// This _should_ be defined by wchar.h, but e.g. OpenBSD doesn't.
 #define WCHAR_MAX INT_MAX

src/iothread.cpp

@@ -491,7 +491,7 @@ static uint64_t next_thread_id() {
 }
 
 uint64_t thread_id() {
-    static thread_local uint64_t tl_tid = next_thread_id();
+    static FISH_THREAD_LOCAL uint64_t tl_tid = next_thread_id();
     return tl_tid;
 }