Remove -ffast-math from default CFLAGS

Fixes glsl-const-folding-01. inversesqrt(1.0) != 1.0 was evaluating as
true.

Signed-off-by: Matt Turner <mattst88@gmail.com>

configure.ac

@@ -176,9 +176,6 @@ esac
 dnl Add flags for gcc and g++
 if test "x$GCC" = xyes; then
     CFLAGS="$CFLAGS -Wall -Wmissing-prototypes -std=c99"
-    if test "x$CLANG" = "xno"; then
-       CFLAGS="$CFLAGS -ffast-math"
-    fi
 
     # Enable -fvisibility=hidden if using a gcc that supports it
     save_CFLAGS="$CFLAGS"