sparcv9: Disable -Wuninitialized warnings breaking bootstrap [PR92002]

sparcv9: Disable -Wuninitialized warnings breaking bootstrap [PR92002]

sparcv9 bootstrap has been broken for 1 1/2 years now by spurious
-Wuninitialized warnings:

In function ‘wide_int wi::max_value(unsigned int, signop)’,
    inlined from ‘wide_int wi::max_value(unsigned int, signop)’ at /vol/gcc/src/hg/master/local/gcc/wide-int.cc:330:1:
/vol/gcc/src/hg/master/local/gcc/wide-int.cc:335:31: error: ‘<anonymous>.generic_wide_int<wide_int_storage>::<anonymous>.wide_int_storage::val[1]’ may be used uninitialized [-Werror=maybe-uninitialized]
  335 |     return shwi (-1, precision);
      |                               ^
[...]
In function ‘wide_int get_nonzero_bits(const_tree)’,
    inlined from ‘wide_int get_nonzero_bits(const_tree)’ at /vol/gcc/src/hg/master/local/gcc/tree-ssanames.c:531:1:
/vol/gcc/src/hg/master/local/gcc/tree-ssanames.c:544:67: error: ‘<anonymous>.generic_wide_int<wide_int_storage>::<anonymous>.wide_int_storage::val[1]’ may be used uninitialized [-Werror=maybe-uninitialized]
  544 |                          | (HOST_WIDE_INT) pi->misalign, precision);
      |                                                                   ^
[...]

Before we ship yet another release with this issue, I suggest to at
least include a workaround of demoting them to warnings.

Tested on sparcv9-sun-solaris2.11.

2021-03-03  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	gcc:
	PR bootstrap/92002
	* config/sparc/t-sparc (tree-ssanames.o-warn): Don't error for
	-Wuninitialized, -Wmaybe-uninitialized.
	(wide-int.o-warn): Likewise.