[TSan] Build TSan runtime with -fPIE.

This removes all register spills from the performance-critical __tsan_{read,write}{1,2,4,8} functions when the host compiler is GCC.

llvm-svn: 178340

compiler-rt/lib/tsan/CMakeLists.txt

@@ -2,8 +2,11 @@
 
 include_directories(..)
 
+# SANITIZER_COMMON_CFLAGS contains -fPIC, but it's performance-critical for
+# TSan runtime to be built with -fPIE to reduce the number of register spills.
 set(TSAN_CFLAGS
   ${SANITIZER_COMMON_CFLAGS}
+  -fPIE
   -fno-rtti)
 # FIXME: Add support for compile flags:
 #   -Wframe-larger-than=512,