fix build with gcc < 4.9

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>

src/cc/CMakeLists.txt

@@ -9,7 +9,9 @@ BISON_TARGET(Parser parser.yy ${CMAKE_CURRENT_BINARY_DIR}/parser.yy.cc COMPILE_F
 FLEX_TARGET(Lexer lexer.ll ${CMAKE_CURRENT_BINARY_DIR}/lexer.ll.cc COMPILE_FLAGS "--c++ --o lexer.ll.cc")
 ADD_FLEX_BISON_DEPENDENCY(Lexer Parser)
 
-set(CMAKE_SHARED_LINKER_FLAGS "-static-libstdc++ -Wl,--exclude-libs=ALL")
+# if gcc 4.9 or higher is used, static libstdc++ is a good option
+#set(CMAKE_SHARED_LINKER_FLAGS "-static-libstdc++ -Wl,--exclude-libs=ALL")
+set(CMAKE_SHARED_LINKER_FLAGS "-Wl,--exclude-libs=ALL")
 
 add_library(bpfprog SHARED bpf_common.cc bpf_module.cc codegen_llvm.cc
   node.cc parser.cc printer.cc type_check.cc libbpf.c b_frontend_action.cc

src/cc/kbuild_helper.h

@@ -57,6 +57,10 @@ class DirStack {
   char cwd_[256];
 };
 
+static int ftw_cb(const char *path, const struct stat *, int) {
+  return ::remove(path);
+}
+
 // Scoped class to manage the creation/deletion of tmpdirs
 class TmpDir {
  public:
@@ -69,10 +73,7 @@ class TmpDir {
       ok_ = true;
   }
   ~TmpDir() {
-    auto fn = [] (const char *path, const struct stat *, int) -> int {
-      return ::remove(path);
-    };
-    if (::ftw(prefix_.c_str(), fn, 20) < 0)
+    if (::ftw(prefix_.c_str(), ftw_cb, 20) < 0)
       ::perror("ftw");
     else
       ::remove(prefix_.c_str());