[nolibc] Begin moving sanitizer_common's libc-dependent code to a separate library

Introduce a new object library, RTSanitizerCommonLibc, which will contain
the subset of sanitizer_common with libc dependencies. RTSanitizerCommon
contains the remainder of sanitizer_common, and is intended to have no
libc dependencies. Begin moving code to RTSanitizerCommonLibc, starting
with sanitizer_common.cc, whose libc-dependent portion is moved to
sanitizer_common_libcdep.cc, the first member of the new library.

This split affects the CMake build only.  The makefile build continues
to produce the full sanitizer_common library.

llvm-svn: 182118
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_common.h b/compiler-rt/lib/sanitizer_common/sanitizer_common.h
index 252224f..f0208f3 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_common.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_common.h
@@ -114,6 +114,8 @@
 void SetPrintfAndReportCallback(void (*callback)(const char *));
 // Can be used to prevent mixing error reports from different sanitizers.
 extern StaticSpinMutex CommonSanitizerReportMutex;
+void MaybeOpenReportFile();
+extern fd_t report_fd;
 
 uptr OpenFile(const char *filename, bool write);
 // Opens the file 'file_name" and reads up to 'max_len' bytes.