AC_LIB_HAVE_LINKFLAGS: linking with static library on macOS

[Mohammad Akhlaghi]

Dear Gnulib,

In Gnuastro, we recently changed to using `AC_LIB_HAVE_LINKFLAGS' for 
all our library dependencies at configure time.

But while testing it on a macOS machine yesterday we came up with the 
following problem:

The machine only has a static version of one of the libraries in 
`/usr/local/lib' (which is also the default `--prefix'). So the output 
of `AC_LIB_HAVE_LINKFLAGS' for that library was a static file 
(`/usr/local/lib/libcfitsio.a') and configure finished without a problem.

But during Make, we got the following crash from `ranlib' when it was 
trying to compile Gnuastro's library (which links with libcfitsio):

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib: 
archive member: .libs/libgnuastro.a(libcfitsio.a) fat file for cputype 
(7) cpusubtype (3) is not an object file (bad magic number)
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ar: 
internal ranlib command failed

The full outputs of `configure' and `make', as well as `config.log' are 
also attached.

After some investigation, I came up with [1] which says: "The root cause 
of it is what we provide static libraries on OS X only in fat(Universal 
binary) format and GNU libtool does not know anything about it. Our 
recommendation here is to use libtool which is provided by Apple in 
XCode.".

Previously (when we were simply using `AC_SEARCH_LIBS'), it would set 
`-lcfitsio' and the linker would go searching in other parts of the 
system and find the a shared library version of libcfitsio. So it 
wouldn't crash, but was building with a library that we didn't know 
about (also not good!)!!!

I wanted to see if know of a solution for such scenarios?

If not, one thing I can currently think of is to add a test within 
`AC_LIB_HAVE_LINKFLAGS' so when it finds a static library, tries linking 
it with a test library, and only use the static library if there is no 
`ranlib' crash.

Thanks a lot in advance,
Mohammad


[1] 
https://software.intel.com/en-us/forums/intel-integrated-performance-primitives/topic/596272

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