x86/vdso: Move DISABLE_BRANCH_PROFILING into the vdso makefile

DISABLE_BRANCH_PROFILING turns off branch profiling (i.e. a
redefinition of 'if').  Branch profiling depends on a bunch of
kernel-internal symbols and generates extra output sections, none of
which are useful or functional in the vDSO.

It's currently turned off for vclock_gettime.c, but vgetcpu.c also
triggers branch profiling, so just turn it off in the makefile.

This fixes the build on some configurations: the vdso could contain
undefined symbols, and the fake section table overflowed due to
ftrace's added sections.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/bf1ec29e03b2bbc081f6dcaefa64db1c3a83fb21.1403642755.git.luto@amacapital.net


Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>