mesa: make use of HAVE_FUNC_ATTRIBUTE_ALIAS macro

We must make sure that xserver has an equivalent one-line
change to its configure.ac as the glx/glapi headers get copied over.

Then again, xserver does _not_ seem to set HAVE_ALIAS to begin with so
one might want to look into that first.

Cc: Adam Jackson <ajax@redhat.com>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
diff --git a/configure.ac b/configure.ac
index e6b4d8c..b68b51e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1776,7 +1776,6 @@
     # Platform specific settings and drivers to build
     case "$host_os" in
     linux*)
-        DEFINES="$DEFINES -DHAVE_ALIAS"
         if test "x$enable_dri3" = xyes; then
             DEFINES="$DEFINES -DHAVE_DRI3"
         fi
@@ -1790,19 +1789,13 @@
             ;;
         esac
         ;;
-    *freebsd* | dragonfly* | *netbsd* | openbsd*)
-        DEFINES="$DEFINES -DHAVE_ALIAS"
-        ;;
-    gnu*)
-        DEFINES="$DEFINES -DHAVE_ALIAS"
-        ;;
     cygwin*)
         if test "x$with_dri_drivers" = "xyes"; then
             with_dri_drivers="swrast"
         fi
         ;;
     darwin*)
-        DEFINES="$DEFINES -DGLX_ALIAS_UNSUPPORTED -DBUILDING_MESA"
+        DEFINES="$DEFINES -DBUILDING_MESA"
         if test "x$with_dri_drivers" = "xyes"; then
             with_dri_drivers="swrast"
         fi