[i386][musl] Add cpuinfo to static libgcc only on *-musl*

[i386][musl] Add cpuinfo to static libgcc only on *-musl*

The __cpu_indicator_init and __cpu_model symbols are not safe to use
from shared libgcc_s.so from ifunc resolvers, so since gcc-6, only
the definitions from static libgcc.a are used, however the symbols
are kept in libgcc_s as well for backward compatibility (with
appropriate symbol version).  On targets without such backward
compatibility concern add cpuinfo to the static library only (this
avoids running the ctor, reduces libgcc_s size and elf abi concerns
about the versioned symbols).

libgcc/
2016-11-11  Szabolcs Nagy  <szabolcs.nagy@arm.com>

	* config.host (i[3456]86-*-musl*, x86_64-*-musl*): Use
	i386/t-cpuinfo-static instead of i386/t-cpuinfo.
	* config/i386/t-cpuinfo-static: New.

From-SVN: r242268