Sync patches from upstream (BSD)

[inkydragon]

• powl returns non-sense results in multi-thread mode #222
• aarch64/fenv: fix fenv_t #319 (comment)

diff: inkydragon@0877489

Do we want to sync openlibm_fenv_arm.h from FreeBSD too?

Seems there are some bugs:

openlibm/include/openlibm_fenv_arm.h

Lines 65 to 67 in 5a88ede

	/* We need to be able to map status flag positions to mask flag positions */
	#define _FPUSW_SHIFT 16
	#define _ENABLE_MASK (FE_ALL_EXCEPT << _FPUSW_SHIFT)

/* We need to be able to map status flag positions to mask flag positions */
#ifndef __ARM_PCS_VFP
#define	_FPUSW_SHIFT	16
#define	_ENABLE_MASK	(FE_ALL_EXCEPT << _FPUSW_SHIFT)
#endif

And FreeBSD doesn't use _ENABLE_MASK freebsd/freebsd-src@de1aa3d/lib/msun/arm/fenv.h#L83-L87

#else	/* __ARM_PCS_VFP */

...

#define _FPU_MASK_SHIFT	8

freebsd/freebsd-src@de1aa3d/lib/msun/arm/fenv.h#L113