compiler-rt: Try to appease lint script.

A bot complains:

/b/sanitizer-x86_64-linux-autoconf/build/llvm/projects/compiler-rt/lib/sanitizer_common/tests/malloc_stress_transfer_test.cpp:2:  Streams are highly discouraged.  [readability/streams] [3]
/b/sanitizer-x86_64-linux-autoconf/build/llvm/projects/compiler-rt/lib/sanitizer_common/tests/sanitizer_libc_test.cpp:11:  Streams are highly discouraged.  [readability/streams] [3]
lib/CMakeFiles/SanitizerLintCheck.dir/build.make:57: recipe for target 'lib/CMakeFiles/SanitizerLintCheck' failed

I do not know why this apparently wasn't a problem when the files
had extension .cc.

llvm-svn: 367493