header detection doesn't work for C++ headers

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What steps will reproduce the problem?
1. make sure Boost headers are installed
2. put something like "config.h_HEADERS = boost/shared_ptr.hpp" in Quagmire.mk
3. run "make"

What is the expected output? What do you see instead?
config.h should have the appropriate HAVE_BOOST_SHARED_PTR_HPP symbol defined, 
but it is 
#undef.

It looks like the problem is that Quagmire/checkheader.mk uses "$(CC) $(CFLAGS) 
$(CPPFLAGS)" to 
do the detection, so it doesn't find the C++ standard headers, which fails the 
test compilation. It 
seems like Quagmire would need something like AC_LANG, or a separate test for 
C++ headers.

Original issue reported on code.google.com by pphaneuf on 16 May 2010 at 8:09