target/ppc: use MAKE_64BIT_MASK for mcrfs exception clear mask

In gen_mcrfs() the FPSCR nibble mask is computed as:
      `~((0xF << shift) & FP_EX_CLEAR_BITS)`

Here, 0xF is of type int, so the left shift is performed in
32-bit signed arithmetic. For bfa=0 we get shift=28,
and (0xF << 28) = 0xF0000000, which is not representable as a 32-bit
signed int. Static analyzers flag this as a potential integer
overflow.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Denis Sergeev <zeff@altlinux.org>
Reviewed-by: Chinmay Rath <rathc@linux.ibm.com>
Signed-off-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Link: https://lore.kernel.org/r/20250915080118.29898-1-zeff@altlinux.org
Message-ID: <20250915080118.29898-1-zeff@altlinux.org>

Author: zeff-ir

target/ppc/translate/fp-impl.c.inc

@@ -396,7 +396,7 @@ static void gen_mcrfs(DisasContext *ctx)
     tcg_gen_extu_tl_i64(tnew_fpscr, cpu_fpscr);
     /* Only the exception bits (including FX) should be cleared if read */
     tcg_gen_andi_i64(tnew_fpscr, tnew_fpscr,
-                     ~((0xF << shift) & FP_EX_CLEAR_BITS));
+                     ~(MAKE_64BIT_MASK(shift, 4) & FP_EX_CLEAR_BITS));
     /* FEX and VX need to be updated, so don't set fpscr directly */
     tmask = tcg_constant_i32(1 << nibble);
     gen_helper_store_fpscr(tcg_env, tnew_fpscr, tmask);