accept empty EM_ASMs

lib/Target/JSBackend/JSBackend.cpp

diff --git a/lib/Target/JSBackend/JSBackend.cpp b/lib/Target/JSBackend/JSBackend.cpp
index 6693eb2..1293384 100644
--- a/lib/Target/JSBackend/JSBackend.cpp
+++ b/lib/Target/JSBackend/JSBackend.cpp
@@ -371,19 +371,24 @@
     unsigned getAsmConstId(const Value *V) {
       V = resolveFully(V);
       const Constant *CI = cast<GlobalVariable>(V)->getInitializer();
-      const ConstantDataSequential *CDS = cast<ConstantDataSequential>(CI);
-      std::string code = CDS->getAsString();
-      // replace newlines quotes with escaped newlines
-      size_t curr = 0;
-      while ((curr = code.find("\\n", curr)) != std::string::npos) {
-        code = code.replace(curr, 2, "\\\\n");
-        curr += 3; // skip this one
-      }
-      // replace double quotes with escaped single quotes
-      curr = 0;
-      while ((curr = code.find('"', curr)) != std::string::npos) {
-        code = code.replace(curr, 1, "\\" "\"");
-        curr += 2; // skip this one
+      std::string code;
+      if (isa<ConstantAggregateZero>(CI)) {
+        code = " ";
+      } else {
+        const ConstantDataSequential *CDS = cast<ConstantDataSequential>(CI);
+        code = CDS->getAsString();
+        // replace newlines quotes with escaped newlines
+        size_t curr = 0;
+        while ((curr = code.find("\\n", curr)) != std::string::npos) {
+          code = code.replace(curr, 2, "\\\\n");
+          curr += 3; // skip this one
+        }
+        // replace double quotes with escaped single quotes
+        curr = 0;
+        while ((curr = code.find('"', curr)) != std::string::npos) {
+          code = code.replace(curr, 1, "\\" "\"");
+          curr += 2; // skip this one
+        }
       }
       if (AsmConsts.count(code) > 0) return AsmConsts[code];
       unsigned id = AsmConsts.size();