Prevent link-time optimization from inlining __gcry_burn_stack

* src/g10lib.h (NOINLINE_FUNC): New attribute macro.
* src/misc.c (__gcry_burn_stack): Add NOINLINE_FUNC attribute.

LTO can cause inline of gcry_burn_stack and result tail-call
to _gcry_fast_wipememory and defeat tail-call prevention in
_gcry_burn_stack macro. Mark gcry_burn_stack with 'noinline'
attribute to prevent unwanted inlining of this function in
LTO builds.

• Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>