fix clobber of edx in i386 vsyscall asm
fix clobber of edx in i386 vsyscall asm

this function does not obey the normal calling convention; like a
syscall instruction, it's expected not to clobber any registers except
the return value. clobbering edx could break callers that were reusing
the value cached in edx after the syscall returns.

chardi/musl,chardi/musl,chardi/musl