mesa: Check that _XOPEN_SOURCE is defined before using it.

diff --git a/src/mesa/main/imports.h b/src/mesa/main/imports.h
index a439370bc4c39686681c1a9a49fc3af900db64b7..e967b14731151b68c579125ff36366283ba95d6a 100644 (file)
--- a/src/mesa/main/imports.h
+++ b/src/mesa/main/imports.h
@@ -120,7 +120,7 @@ typedef union { GLfloat f; GLint i; } fi_type;
  * \name Work-arounds for platforms that lack C99 math functions
  */
 /*@{*/
-#if (_XOPEN_SOURCE < 600) && !defined(_ISOC99_SOURCE) \
+#if (defined(_XOPEN_SOURCE) && (_XOPEN_SOURCE < 600)) && !defined(_ISOC99_SOURCE) \
    && (!defined(__STDC_VERSION__) || (__STDC_VERSION__ < 199901L)) \
    && (!defined(_MSC_VER) || (_MSC_VER < 1400))
 #define acosf(f) ((float) acos(f))