Remove try/catch(...) from Win32/Signals.inc.

catch(...) is used in Win32/Signals.inc for catching Win32 structured
exceptions, but according to [1], this is wrong.

We can't simply change try/catch to __try/__finally, since this syntax is not
supported by MinGW. We can use __try/__finally on MSVC and __try1/__except1
macros on MinGW [2], but I think that that solution obfuscates the code too
much.

The use of try/catch(...) in Signals.inc makes it impossible to link
MinGW-compiled libSystem with llvm-gcc compiled executables. I propose that we
just remove try/catch(...) from Signals.inc, since the meaning of the code won't
change.

[1] http://members.cox.net/doug_web/eh.htm
[2] http://article.gmane.org/gmane.comp.compilers.llvm.cvs/81315

llvm-svn: 117442