mesa: Replace a priori knowledge of gcc builtins with configure tests.

Presumbly this will let clang and other compilers use the built-ins as
well.

Notice two changes specifically:
   - in _mesa_next_pow_two_64(), always use __builtin_clzll and add a
     static assertion that this is safe.
   - in macros.h, remove the clang-specific definition since it should
     be able to detect __builtin_unreachable in configure.

Reviewed-by: Jason Ekstrand <[email protected]> [C bits]
Reviewed-by: Ian Romanick <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp b/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
index 105acdd11b7..844f5e43029 100644
--- a/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
+++ b/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
@@ -1343,7 +1343,7 @@ brw_blorp_blit_program::single_to_blend()
  */
 inline int count_trailing_one_bits(unsigned value)
 {
-#if defined(__GNUC__) && ((__GNUC__ * 100 + __GNUC_MINOR__) >= 304) /* gcc 3.4 or later */
+#ifdef HAVE___BUILTIN_CTZ
    return __builtin_ctz(~value);
 #else
    return _mesa_bitcount(value & ~(value + 1));