Improve -mpreferred-stack-boundary configure message.

Explicitly say we are checking for -mpreferred-stack-boundary=2.
Only 2 is ever used when it is supported. Some gcc versions/arches
(e.g. GCC 4.8 for x86_64) support -mpreferred-stack-boundary, but
only between 4 and 12. The message that -mpreferred-stack-boundary
wasn't supported was a little confusing. So explicitly say we checked
for -mpreferred-stack-boundary=2.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14324 a5019735-40e9-0310-863c-91ae7b9d1cf9
Check some known PATHs for mpicc in configure.

On some distributions (fedora) mpicc not installed on the default PATH.
Add a search path for finding mpicc by default if it is installed.
The user can still override the used mpicc compiler using --with-mpicc=.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14325 a5019735-40e9-0310-863c-91ae7b9d1cf9
exp-sgcheck/tests/hackedbz2.c mark vex_strlen as noinline

Explicitly set noinline so the test can check it is in the backtrace.
Newer gcc versions happily optimize it away otherwise.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14326 a5019735-40e9-0310-863c-91ae7b9d1cf9
Bug 338445 amd64 vbit-test fails with unknown opcodes used by arm64 VEX.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14327 a5019735-40e9-0310-863c-91ae7b9d1cf9
NEWS 330319 vex amd64->IR: unhandled instruction bytes: 0xF 0x1 0xD5 (xend)

VEX svn r2931

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14328 a5019735-40e9-0310-863c-91ae7b9d1cf9
Follow up to r14313: disable stack cache earlier
glibc is recycling memory for detached threads before a thread
termination => disable the stack cache earlier (i.e. once
a 'non main thread' is seen)



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14329 a5019735-40e9-0310-863c-91ae7b9d1cf9