[RFC PATCH 1/4] osdep: Avoid using Clang-specific __builtin_available()

["Philippe Mathieu-Daudé via" <qemu-devel@nongnu.org>]

Replace MAC_OS_X_VERSION_MAX_ALLOWED upper check by the lower
one (MAC_OS_X_VERSION_MIN_REQUIRED) and remove the Clang specific
__builtin_available() to allow building with GCC.

Remove the Clang specific __builtin_available() to allow building
with GCC, otherwise we get:

  include/qemu/osdep.h: In function 'qemu_thread_jit_write':
  include/qemu/osdep.h:787:9: warning: implicit declaration of function '__builtin_available'; did you mean '__builtin_scalbl'? [-Wimplicit-function-declaration]
    787 |     if (__builtin_available(macOS 11.0, *)) {
        |         ^~~~~~~~~~~~~~~~~~~
        |         __builtin_scalbl
  include/qemu/osdep.h:787:9: warning: nested extern declaration of '__builtin_available' [-Wnested-externs]
  include/qemu/osdep.h:787:29: error: 'macOS' undeclared (first use in this function)
    787 |     if (__builtin_available(macOS 11.0, *)) {
        |                             ^~~~~
  include/qemu/osdep.h:787:29: note: each undeclared identifier is reported only once for each function it appears in
  include/qemu/osdep.h:787:34: error: expected ')' before numeric constant
    787 |     if (__builtin_available(macOS 11.0, *)) {
        |                            ~     ^~~~~
        |                                  )

Replace the MAC_OS_X_VERSION_MAX_ALLOWED upper check by a lower
one (with MAC_OS_X_VERSION_MIN_REQUIRED) to avoid on Catalina:

  include/qemu/osdep.h:780:5: warning: 'pthread_jit_write_protect_np' is only available on macOS 11.0 or newer [-Wunguarded-availability-new]
      pthread_jit_write_protect_np(true);
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
  /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/pthread.h:561:6: note: 'pthread_jit_write_protect_np' has been marked as being introduced in macOS 11.0 here, but the deployment target is macOS 10.15.0
  void pthread_jit_write_protect_np(int enabled);
       ^

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 include/qemu/osdep.h | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index d1660d67fa..1e7a002339 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -774,19 +774,15 @@ size_t qemu_get_host_physmem(void);
  * for the current thread.
  */
 #if defined(MAC_OS_VERSION_11_0) && \
-    MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_VERSION_11_0
+    MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_VERSION_11_0
 static inline void qemu_thread_jit_execute(void)
 {
-    if (__builtin_available(macOS 11.0, *)) {
-        pthread_jit_write_protect_np(true);
-    }
+    pthread_jit_write_protect_np(true);
 }
 
 static inline void qemu_thread_jit_write(void)
 {
-    if (__builtin_available(macOS 11.0, *)) {
-        pthread_jit_write_protect_np(false);
-    }
+    pthread_jit_write_protect_np(false);
 }
 #else
 static inline void qemu_thread_jit_write(void) {}
-- 
2.34.1