xtensa: reimplement register spilling

xtensa: reimplement register spilling

Spilling windowed registers in userspace is much easier, more portable,
less error-prone and equally effective as in kernel. Now that register
spilling syscall is considered obsolete in the xtensa linux kernel
replace it with CALL12 followed by series of ENTRY in libgcc.

2015-08-18  Max Filippov  <jcmvbkbc@gmail.com>
libgcc/
	* config/xtensa/lib2funcs.S (__xtensa_libgcc_window_spill): Use
	CALL12 followed by series of ENTRY to spill windowed registers.
	(__xtensa_nonlocal_goto): Call __xtensa_libgcc_window_spill
	instead of making linux spill syscall.

From-SVN: r226962