Can't pass -fsanitize-coverage to scons using CCFLAGS

scons -j12 --mute CC=/usr/local/bin/clang CXX=/usr/local/bin/clang++ CCFLAGS="-fsanitize-coverage=2" --opt=off --allocator=system --sanitize=address --variant-dir=asan mongod unittests

scons: Reading SConscript files ...

scons version: 2.3.4

python version: 2 7 4 'final' 0

Checking whether the C++ compiler works... yes

Checking whether the C compiler works... yes

Checking if C++ compiler "/usr/local/bin/clang++" is GCC... no

Checking if C++ compiler "/usr/local/bin/clang++" is clang... yes

Checking if C compiler "/usr/local/bin/clang" is clang... yes

Detected a x86_64 processor

Checking if target OS linux is supported by the toolchain yes

Checking if C compiler is clang 3.4 (or Apple XCode 5.1.1) or newer...no

Checking if C++ compiler is clang 3.4 (or Apple XCode 5.1.1) or newer...no

ERROR: Refusing to build with compiler that does not meet requirements

See /mnt/hdd/mongo-copy/build/scons/config.log for details