Update some of the amd64 parts of libc:

Update some of the amd64 parts of libc:

* Change the syscall stub branch orders so that the static branch
prediction will assume that syscalls will succeed rather than fail.

* Add error handling for PSEUDO syscalls.

* Add END() macros for Assembler code. This causes the symbol
table to include the size of the function.

* ldexp:  Fix a typo in the !__GNUC__ case and remove an obsolete
comment.

* setjmp/longjmp changes:
-Save and restore the control part of the MXCSR in addition to the
i387 control word to ensure that the two are consistent.
-Don't clobber the FPU exception flags in longjmp. C99 requires them
to remain unchanged.

Obtained-from: FreeBSD