Manual update of LLVM_MAIN_REVISION to 551331 (llvm#3915)

Author: ronlieb

llvm/include/llvm/Config/llvm-config.h.cmake

@@ -17,7 +17,7 @@
 /* The number of commits in the linear history from the
  * start of the universe up to the latest llvm main commit
  * that has been merged */
-#define LLVM_MAIN_REVISION 550353
+#define LLVM_MAIN_REVISION 551331
 
 /* Define if LLVM_ENABLE_DUMP is enabled */
 #cmakedefine LLVM_ENABLE_DUMP