Oh, you are right, it's not upstream. It's actually applied to Homebrew (https://brew.sh/) libtool formula which is where I originally got libtool.m4, see:

I see your point. I'd like to locate/identify where the change comes from.
I think that what you refer by "new libtool.m4" is actually macOS local change (I mean, not from libtool upstream, AFAIK).
Could you please point out the source of the change?

That would work, however we might hit this issue with a new macOS release. Would it make more sense to update to what the new libtool.m4 is doing? Linker flags are the same, it only changes the way they detect macOS versions:

That does indeed not look like something which could introduce a regression.

I misunderstood as if we need to update libtool from upstream.

macOS has low priority for us and I do not want to risk any regression.

About merging our local changes.

We have our own changes for ltmain.sh and libtool.m4.

And update from automake 1.16:

It's better to update the set of files from libtool:

build-aux/ltmain.sh
m4/libtool.m4
m4/ltoptions.m4
m4/ltsugar.m4
m4/ltversion.m4
m4/lt~obsolete.m4

Our libtool was 2.4.2 + Debian patches + our local changes.
Debian patches are:
https://salsa.debian.org/mckinstry/libtool/-/blob/debian/master/debian/patches/link_all_deplibs.patch
https://salsa.debian.org/mckinstry/libtool/-/blob/debian/master/debian/patches/netbsdelf.patch

It is my confusion. The API is available. I only looked for symbols in the library.
It is #define-d macro to pthread_cond_*.

For Windows, it is available. I don't know the reason why it has not been available for POSIX.

While I think that building with GCC 4 on Solaris 11/12 is minor issue, requirement of newer POSIX API (on GNU/Linux) would be a bit serious issue.
I pushed my change to fix this.

While original npth-1.6 can be compiled with newer gcc (>= 5), we'd say please use CFLAGS+=-std=gnu99 with older gcc, as workaround.

I figured out:

• Removing -D_POSIX_C_SOURCE=200112L works both of gcc 4.9 and gcc 5.5 on Solaris 11.3 (even with -std=c99).
• Then, adding -D_XOPEN_SOURCE=500, gcc 4.9 works, but gcc 5.5 failed by another error (Compiler or options invalid for pre-UNIX 03 X/Open applications and pre-2001 POSIX applications)
  • I confirmed gcc 5.5 defaults to -std=gnu99

Thanks for your offer. I have an account for GCC Compiler Farm. I'm trying with gcc211 machine. will back soon.

In case of gcc 4.8 on Solaris, could you please try this patch (instead of configure patch) to see if it works?

It looks like somewhat complicated more. It seems that specifying _POSIX_C_SOURCE=200112L is not good on Solaris with old GCC. Perhaps, it would have no problem with newer gcc (or -std=gnu99 option).

IIUC, -std=c99 won't solve this issue. It is Solaris specific C99 issue.

It looks like Solaris only needs CFLAGS+=-std=c99. It was added for all programs and libraries listed at https://www.gnupg.org/download/index.html.

OK, it's a libc with no pthread_rwlock_t.

New gpg-error.m4 detects gpgrt-config, too.
And configure supplies --libdir when it invokes gpgrt-config.
For other *.m4 (libassuan, ksba, libgcrypt, ntbtls), it is possible for them to check GPGRT_CONFIG to use gpgrt-config if any.
For npth.m4, it can do that too, with no hard dependency to libgpg-error.

A bit tricky, but this would be good to use gpgrt-config by gpg-error.m4.
I say "tricky", because its name is gpg-error.m4 but it configure GPGRT_CONFIG to access to GPG_ERROR_CONFIG.

It might be good idea to provide libgcrypt.pc in libgcrypt 1.8.x for forward compatibility with libgpg-error 1.33.

Well, I changed my mind. Use of new gpgrt-config requires software update to introduce gpgrt.m4 and update of configure.ac to switch gpgrt from gpg-error, in standard way.
That's too much this time. It's good to defer this change.

OK, I'll change to use gpgrt-config, along with requiring newer version of libgpg-error.

May I suggest to use a (new) gpgrt-config instead of the current name libgpg-error-config. The long term plan is to change the name of the library.

This is the dependency graph: