tools/clang/json: Escape strings properly

When preparing a codesearch index, I encountered errors which I narrowed
down to lines like the following in the json output of codesearch:

  "type": "void (void  __attribute__((btf_type_tag("user")))*, const void *, size_t, size_t)",

After this change, the line gets formatted like this:

  "type": "void (void  __attribute__((btf_type_tag(\"user\")))*, const void *, size_t, size_t)",

This fixes the errors I encountered

Author: FlorentRevest

tools/clang/json.h

@@ -52,11 +52,33 @@ class JSONPrinter {
   Scope Top;
 };
 
+inline void print(JSONPrinter& Printer, const char* V) {
+  printf("\"");
+  if (V) {
+    for (; *V; ++V) {
+      switch (*V) {
+      case '"': printf("\\\""); break;
+      case '\\': printf("\\\\"); break;
+      case '\b': printf("\\b"); break;
+      case '\f': printf("\\f"); break;
+      case '\n': printf("\\n"); break;
+      case '\r': printf("\\r"); break;
+      case '\t': printf("\\t"); break;
+      default:
+        if ((unsigned char)*V < 0x20)
+          printf("\\u%04x", (unsigned char)*V);
+        else
+          printf("%c", *V);
+      }
+    }
+  }
+  printf("\"");
+}
+
 inline void print(JSONPrinter& Printer, int V) { printf("%d", V); }
 inline void print(JSONPrinter& Printer, unsigned V) { printf("%u", V); }
 inline void print(JSONPrinter& Printer, int64_t V) { printf("%ld", V); }
 inline void print(JSONPrinter& Printer, bool V) { printf("%s", V ? "true" : "false"); }
-inline void print(JSONPrinter& Printer, const char* V) { printf("\"%s\"", V ? V : ""); }
 inline void print(JSONPrinter& Printer, const std::string& V) { print(Printer, V.c_str()); }
 
 template <typename E> void print(JSONPrinter& Printer, const std::unique_ptr<E>& V) {