[compiler-rt] Fix cmake warnings

 - Fix cmake BOOL misspellings
 - Set cmake policy for CMP0075 to NEW

As requested by smeenai I've compared CMAkeCache.txt in master with and
without this patch and the only changes are to the variable types I fixed:

     $ diff build-b1-master/CMakeCache.txt build-b1-compiler-rt-fix-cmake-warnings/CMakeCache.txt
     503c503
     < COMPILER_RT_BAREMETAL_BUILD:STRING=OFF
     ---
     > COMPILER_RT_BAREMETAL_BUILD:BOOL=OFF
     550c550
     < COMPILER_RT_HWASAN_WITH_INTERCEPTORS:STRING=ON
     ---
     > COMPILER_RT_HWASAN_WITH_INTERCEPTORS:BOOL=ON

Patch by Wink Saville <wink@saville.com>.

Differential Revision: https://reviews.llvm.org/D61203

llvm-svn: 361866