Cygwin: fix new sigfe.o generation in optimized case

Cygwin: fix new sigfe.o generation in optimized case

Commit 0597c84b9bdb ("Cygwin: revamp TLS offsets computation")
introduced a really weird problem when building Cygwin with
optimization.

First of all, the tlsoffsets file is broken with -O2.  This
can easily be fixed by running the compiler with -O0 when called
from the gentls_offsets script.

But it gets worse:

When creating sigfe.o with optimization, the generated machine code
uses incorrect offsets: For some reason the assembler codes using
_cygtls.stackptr as offset value are assembled into machine code
using _cygtls.pstackptr as offsets.

And as if that isn't already absurd enough, renaming _cygtls.pstackptr
to, say, _cygtls.blurb, fixes the assembled machine code expressions;
they use the value of _cygtls.stackptr again.

So I changed gentls_offsets and gendef to use _cygtls.foo_p rather
than _cygtls.pfoo and that fixes the assembled code in the optimized
case.

No, I can't explain that.  There's no system in that behaviour.
It looks absolutely crazy.

Fixes: 0597c84b9bdb ("Cygwin: revamp TLS offsets computation")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>