[Patch, PowerPC/Darwin] Fix library export of long double symbols.

[Patch, PowerPC/Darwin] Fix library export of long double symbols.

During 8.x, the rs6000 target-specific mangling was reorganised which uncovered
a long-standing bug in Darwin’s mangling for ‘IBM’ long double.  Now the symbols
are correctly mangled, and we end up with a bunch of test link fails.

This patch adds the necessary subset of the Linux long double exports to Darwin’s
export table.

2018-12-22  Iain Sandoe  <iain@sandoe.co.uk>

	* /config/os/bsd/darwin/ppc-extra.ver: Append long double symbols.

From-SVN: r267358