[PATCH 1/2] build: please Clang++ 3.2+ on Flex scanners

[Akim Demaille]

Clang++, with -Wall, rejects code generated by Flex (for C scanners):

  CXX      examples/calc++/examples_calc___calc__-calc++-scanner.o
  In file included from examples/calc++/calc++-scanner.cc:1:
  error: implicit conversion of NULL constant to 'bool' 
[-Werror,-Wnull-conversion]
  if ( ! ( (yy_buffer_stack) ? (yy_buffer_stack)[(yy_buffer_stack_top)] : 
__null) ) {
       ~                                                                  ^~~~~~
                                                                          false
* configure.ac (WARN_NO_NULL_CONVERSION_CXXFLAGS): Compute it.
* examples/calc++/local.mk (examples_calc___calc___CXXFLAGS): Use it.
---
 configure.ac             | 2 ++
 examples/calc++/local.mk | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/configure.ac b/configure.ac
index 76a0ecf..289b299 100644
--- a/configure.ac
+++ b/configure.ac
@@ -133,6 +133,8 @@ if test "$enable_gcc_warnings" = yes; then
   # Warnings for the test suite only.
   gl_WARN_ADD([-Wundef], [WARN_CXXFLAGS_TEST])
   gl_WARN_ADD([-pedantic], [WARN_CXXFLAGS_TEST])
+  # Clang++ 3.2+ reject C code generated by Flex.
+  gl_WARN_ADD([-Wno-null-conversion], [WARN_NO_NULL_CONVERSION_CXXFLAGS])
   # Variants break strict aliasing analysis.
   gl_WARN_ADD([-fno-strict-aliasing], [NO_STRICT_ALIAS_CXXFLAGS])
   CXXFLAGS=$save_CXXFLAGS
diff --git a/examples/calc++/local.mk b/examples/calc++/local.mk
index c0cb5e8..6eb31f8 100644
--- a/examples/calc++/local.mk
+++ b/examples/calc++/local.mk
@@ -69,5 +69,7 @@ nodist_examples_calc___calc___SOURCES =               \
   $(calc_sources)
 
 examples_calc___calc___CPPFLAGS = -I$(top_builddir)/examples/calc++
+examples_calc___calc___CXXFLAGS =                      \
+  $(AM_CXXFLAGS) $(WARN_NO_NULL_CONVERSION_CXXFLAGS)
 dist_TESTS += examples/calc++/calc++.test
 endif
-- 
1.8.1.1