[sancov] Name the global containing the main source file name

If the global name doesn't start with __sancov_gen, ASan will insert
unecessary red zones around it.

llvm-svn: 287117
diff --git a/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp b/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
index 031effb..730e28a 100644
--- a/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
+++ b/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
@@ -357,9 +357,9 @@
   // Create variable for module (compilation unit) name
   Constant *ModNameStrConst =
       ConstantDataArray::getString(M.getContext(), M.getName(), true);
-  GlobalVariable *ModuleName =
-      new GlobalVariable(M, ModNameStrConst->getType(), true,
-                         GlobalValue::PrivateLinkage, ModNameStrConst);
+  GlobalVariable *ModuleName = new GlobalVariable(
+      M, ModNameStrConst->getType(), true, GlobalValue::PrivateLinkage,
+      ModNameStrConst, "__sancov_gen_modname");
   if (Options.TracePCGuard) {
     if (HasSancovGuardsSection) {
       Function *CtorFunc;