hhvm: fix build

Upstream re2 commit:

b94b7cd42e

Upstream bytecode.h commit:

f8a75ca667

pkgs/development/compilers/hhvm/default.nix

@@ -26,6 +26,10 @@ stdenv.mkDerivation rec {
       gmp libyaml libedit libvpx imagemagick fribidi gperf
     ];
 
+  patches = [
+    ./flexible-array-members-gcc6.patch
+  ];
+
   enableParallelBuilding = false; # occasional build problems;
   dontUseCmakeBuildDir = true;
   NIX_LDFLAGS = "-lpam -L${pam}/lib";

pkgs/development/compilers/hhvm/flexible-array-members-gcc6.patch

@@ -0,0 +1,33 @@
+diff --git a/hphp/runtime/vm/bytecode.h b/hphp/runtime/vm/bytecode.h
+index ddc7b69..edf807c 100644
+--- a/hphp/runtime/vm/bytecode.h
++++ b/hphp/runtime/vm/bytecode.h
+@@ -124,7 +124,7 @@ private:
+   static void* allocMem(unsigned nargs);
+
+ private:
+-  TypedValue m_extraArgs[];
++  TypedValue m_extraArgs[0];
+   TYPE_SCAN_FLEXIBLE_ARRAY_FIELD(m_extraArgs);
+ };
+
+diff --git a/third-party/re2/src/re2/dfa.cc b/third-party/re2/src/re2/dfa.cc
+index 483f678..3aa3610 100644
+--- a/third-party/re2/src/re2/dfa.cc
++++ b/third-party/re2/src/re2/dfa.cc
+@@ -101,8 +101,13 @@ class DFA {
+     uint flag_;         // Empty string bitfield flags in effect on the way
+                         // into this state, along with kFlagMatch if this
+                         // is a matching state.
+-    std::atomic<State*> next_[];    // Outgoing arrows from State,
+-                        // one per input byte class
++// Work around the bug affecting flexible array members in GCC 6.1 and 6.2.
++// (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70932)
++#if !defined(__clang__) && defined(__GNUC__) && __GNUC__ == 6 && __GNUC_MINOR__ >= 1
++    std::atomic<State*> next_[0];   // Outgoing arrows from State, one per input byte class
++#else
++    std::atomic<State*> next_[];    // Outgoing arrows from State, one per input byte class
++#endif
+   };
+
+   enum {