[clang-proto-fuzzer] Allow user-specified compiler arguments.

[morehouse]

Summary

Arguments can be specified after -ignore_remaining_args=1 to modify
the compiler invocation. For example, the following command-line
will fuzz LLVM with a custom optimization level and target triple:

clang-proto-fuzzer CORPUS/ -ignore_remaining_args -O3 \
    -triple arm64-apple-ios9

[vitalybuka]

clang/tools/clang-fuzzer/ExampleClangProtoFuzzer.cpp

33

maybe just strcmp

35

you can put second loop inside of the if just before the break and avoid top level var "I"

[morehouse]

• Refactor and use strcmp.

[kcc]

Update the README file please (with a text similar to this commit message)

cfe/trunk/tools/clang-fuzzer/ExampleClangProtoFuzzer.cpp

32 ↗

(On Diff #111715)

[remark, feel free to ignore]
the "break;" here is redundant, and thus the {} too, i.e. you can keep the code shorter.
Whether it will make it more readable is debatable.

clang/tools/clang-fuzzer/ExampleClangProtoFuzzer.cpp

 //===----------------------------------------------------------------------===//
 
 #include "cxx_proto.pb.h"
 #include "handle-cxx/handle_cxx.h"
 #include "proto-to-cxx/proto_to_cxx.h"
 
 #include "src/libfuzzer/libfuzzer_macro.h"
 
+#include <cstring>
+
 using namespace clang_fuzzer;
 
+static std::vector<const char *> CLArgs;
+
+extern "C" int LLVMFuzzerInitialize(int *argc, char ***argv) {
+  CLArgs.push_back("-O2");
+  for (int I = 1; I < *argc; I++) {
+    if (strcmp((*argv)[I], "-ignore_remaining_args=1") == 0) {
+      for (I++; I < *argc; I++)
+        CLArgs.push_back((*argv)[I]);
+      break;
+    }
+  }
+  return 0;
+}
+
 DEFINE_BINARY_PROTO_FUZZER(const Function& input) {
   auto S = FunctionToString(input);
-  HandleCXX(S, {"-O2"});
+  HandleCXX(S, CLArgs);
 }