[PATCH 2/2] Makefile: use curl-config --cflags

We add the result of "curl-config --libs" when linking curl programs, but we never bother calling "curl-config --cflags". Presumably nobody noticed because:

  - a system libcurl installed into /usr/include/curl wouldn't need any
    flags ("/usr/include" is already in the search path, and the
    #include lines all look <curl/curl.h>, etc).

  - using CURLDIR sets up both the includes and the library path

However, if you prefer CURL_CONFIG to CURLDIR, something simple like:

  make CURL_CONFIG=/path/to/curl-config

doesn't work. We'd link against the libcurl specified by that program, but not find its header files when compiling.

Let's invoke "curl-config --cflags" similar to the way we do for "--libs". Note that we'll feed the result into BASIC_CFLAGS. The rest of the Makefile doesn't distinguish which files need curl support during compilation and which do not. That should be OK, though. At most this should be adding a "-I" directive, and this is how CURLDIR already behaves. And since we follow the immediate-variable pattern from CURL_LDFLAGS, we won't accidentally invoke curl-config once per compilation.

Signed-off-by: Jeff King <peff@peff.net>
---
I didn't bother touching configure.ac here, because I don't think it
would do anything useful. The existing configure script will run
"curl-config --libs" to set CURL_LDFLAGS, suppressing the call to
curl-config inside the Makefile. But with the caveat that you can
convince it to pass something besides --libs (though what would be
useful there, I have no idea, and the commit introducing it didn't shed
any light). So following that pattern, at most we'd just be trading a
call during configure time for one inside the Makefile.

What _could_ be useful is if the configure script used curl-config as part of it's check of whether we have libcurl at all. But it doesn't. We don't even look for curl-config until we've been able to link against -lcurl. I have a feeling this could be fixed by reversing the order of the blocks, but I'm not sure of all of the subtle interactions with CURLDIR. And I don't care enough about autoconf to puzzle it out. We certainly aren't making anything worse with this patch.

 Makefile | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)