[llvm-shlib] Fix the i686 MSVC triple check for listing symbols to export in LLVM-C.dll

https://reviews.llvm.org/D47381 / eb46c95c
changed the triples set up by GetHostTriple.cmake for i686 MSVC
from i686-pc-win32 to i686-pc-windows-msvc without changing
the corresponding condition in llvm-shlib.

Since then, the 32 bit x86 build of LLVM-C.dll has contained no
exported symbols at all.

Differential Revision: https://reviews.llvm.org/D109493