Fix most of LLVM's tests with LLVM_ENABLE_PIC=OFF

Lots of tests rely on llvm-lto being present, but LLVM_ENABLE_PIC=OFF currently
disables building that executable.

There's no reason for not building llvm-lto with LLVM_ENABLE_PIC=OFF so just
build it. r191042 moved it into a "if (!WIN)" block at the time, and then
211852 made that "if(NOT CYGWIN AND LLVM_ENABLE_PIC)" -- but that's only needed
for LTO (the ld64 plugin), not for the llvm-lto binary.

Differential Revision: https://reviews.llvm.org/D56801

llvm-svn: 351374