amd64/-current doesn't compile with clang

[Thomas Klausner]

--- toom44_mul.o ---
/archive/foreign/src/external/lgpl3/gmp/lib/libgmp/../../dist/mpn/generic/toom44_mul.c:209:52:
 error: '&' within '|' [-Werror,-Wbitwise-op-parentheses]
  flags = (enum toom7_flags) (flags | toom7_w3_neg & mpn_toom_eval_dgr3_pm1 
(apx, amx, ap, n, s, tp));
                                    ~ 
~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/archive/foreign/src/external/lgpl3/gmp/lib/libgmp/../../dist/mpn/generic/toom44_mul.c:209:52:
 note: place parentheses around the '&' expression to silence this warning
  flags = (enum toom7_flags) (flags | toom7_w3_neg & mpn_toom_eval_dgr3_pm1 
(apx, amx, ap, n, s, tp));
                                                   ^
                                      (                                         
                    )