libphobos: Fix linker warning and SEGV in core.thread tests.

libphobos: Fix linker warning and SEGV in core.thread tests.

The monolithic core/threadasm.S source has been removed, and split into
multiple parts, one for each intended target CPU/OS.

Added .type and .size directives for all asm implementations of
fiber_switchContent and callWithStackShell where they were missing.

libphobos/ChangeLog:

2019-04-25  Iain Buclaw  <ibuclaw@gdcproject.org>

	PR d/90086
	* m4/druntime/cpu.m4 (DRUNTIME_CPU_SOURCES): New macro.
	* configure.ac: Use it.
	* configure: Regenerate.
	* libdruntime/Makefile.am: Add new config sources to
	DRUNTIME_SOURCES_CONFIGURED.
	* libdruntime/Makefile.in: Regenerate.
	* libdruntime/config/aarch64/switchcontext.S: New file.
	* libdruntime/config/arm/switchcontext.S: New file.
	* libdruntime/config/common/threadasm.S: New file.
	* libdruntime/config/mingw/switchcontext.S: New file.
	* libdruntime/config/mips/switchcontext.S: New file.
	* libdruntime/config/powerpc/switchcontext.S: New file.
	* libdruntime/config/powerpc64/callwithstack.S: New file.
	* libdruntime/config/x86/switchcontext.S: New file.
	* libdruntime/core/threadasm.S: Remove.

From-SVN: r270560