mesa: fix MSVC bitshift overflow warnings

In the BITFIELD_MASK() macro, if b==32 the expression evaluates to
~0u, but the compiler still sees the expression (1 << 32) in the
unused part and issues a warning about integer bitshift overflow.

Fix that by using (b) % 32 to ensure the max shift is 31 bits.

This issue has been present for a while, but shows up much more
often because of the recent VBO changes.

Reviewed-by: Mathias Fröhlich <mathias.froehlich@web.de>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>

src/mesa/main/mtypes.h

@@ -59,7 +59,7 @@ extern "C" {
 #define BITFIELD_BIT(b)      ((GLbitfield)1 << (b))
 /** Set all bits up to excluding bit b */
 #define BITFIELD_MASK(b)      \
-   ((b) == 32 ? (~(GLbitfield)0) : BITFIELD_BIT(b) - 1)
+   ((b) == 32 ? (~(GLbitfield)0) : BITFIELD_BIT((b) % 32) - 1)
 /** Set count bits starting from bit b  */
 #define BITFIELD_RANGE(b, count) \
    (BITFIELD_MASK((b) + (count)) & ~BITFIELD_MASK(b))