[PATCH] Fix LLVMExports.cmake generation with `configure --enable-shared`

[Dan Liew via llvm-commits]

Hi,

At a glance these patches look good. Thanks for tackling this so quickly.

I've given a try and it seems to work. My only comments would be that
the the LLVM_LIBS_TO_EXPORTED in Makefile.llvmbuild. Contains
``gtest`` and ``gtest_main`` which they probably shouldn't given the
variable's name. The ``cmake/modules/Makefile`` has some logic to
remove this but perhaps we should consider preventing LLVMBuild from
exporting gtest and gtest_main instead? CC'ing Takumi because, Takumi
raised this issue a while ago [1].

[1] http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20150706/285465.html