util/format: Generate floating point constants for clamping.

util/format: Generate floating point constants for clamping.

This commit causes the generated C code to change as

            union util_format_r32g32b32a32_sscaled pixel;
  -         pixel.chan.r = (int32_t)CLAMP(src[0], -2147483648, 2147483647);
  -         pixel.chan.g = (int32_t)CLAMP(src[1], -2147483648, 2147483647);
  -         pixel.chan.b = (int32_t)CLAMP(src[2], -2147483648, 2147483647);
  -         pixel.chan.a = (int32_t)CLAMP(src[3], -2147483648, 2147483647);
  +         pixel.chan.r = (int32_t)CLAMP(src[0], -2147483648.0f, 2147483647.0f);
  +         pixel.chan.g = (int32_t)CLAMP(src[1], -2147483648.0f, 2147483647.0f);
  +         pixel.chan.b = (int32_t)CLAMP(src[2], -2147483648.0f, 2147483647.0f);
  +         pixel.chan.a = (int32_t)CLAMP(src[3], -2147483648.0f, 2147483647.0f);
            memcpy(dst, &pixel, sizeof pixel);

which surprisingly makes a difference for MSVC.

Thanks to Juraj Svec for diagnosing this and drafting a fix.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=29661