[cmake] Remove duplicate command line options from build
[cmake] Remove duplicate command line options from build

CMAKE_CXX_FLAGS was added twice to the command line. This causes the command 
line options to be doubled which works until it doesn't as not all options 
can be specified twice. 

For example,

clang-cl foo.c /GS- /GS- -mllvm -small-loop-cost=1 -mllvm -small-loop-cost=1
clang (LLVM option parsing): for the -small-loop-cost option: may only occur zero or one times!


git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@329817 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt