x86: vget_cycles() __always_inline

Mark vget_cycles() as __always_inline, so gcc is never tempted to make
the vsyscall vread_tsc() dive into kernel text, with resulting SIGSEGV.

This was a self-inflicted wound: I've not seen that happen with unhacked
sources; but for debug reasons I'd changed my x86/Makefile to compile
no-unit-at-a-time, and that in conjunction with OPTIMIZE_INLINING=y
ended up with vget_cycles() in kernel text.  Perhaps it can happen
in other ways: safer to use __always_inline.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/asm-x86/tsc.h

@@ -32,7 +32,7 @@ static inline cycles_t get_cycles(void)
 	return ret;
 }
 
-static inline cycles_t vget_cycles(void)
+static __always_inline cycles_t vget_cycles(void)
 {
 	/*
 	 * We only do VDSOs on TSC capable CPUs, so this shouldnt