xemacs @21.4.22: error: implicitly declaring library function 'exit'

[wealthychef1]

xemacs fails to install for me using MacPorts 2.6.4 on Big Sur:

--->  Attempting to fetch xemacs-mule-sumo-2010-07-27.tar.gz from https://lil.fr.distfiles.macports.org/xemacs
--->  Verifying checksums for xemacs
--->  Extracting xemacs
--->  Applying patches to xemacs
--->  Configuring xemacs
Error: Failed to configure xemacs, consult /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_editors_xemacs/xemacs/work/xemacs-21.4.22/config.log
Error: Failed to configure xemacs: configure failure: command execution failed
Error: See /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_editors_xemacs/xemacs/main.log for details.

root@Richs-iMac (~ ): grep error /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_editors_xemacs/xemacs/work/xemacs-21.4.22/config.log
configure:2412:10: fatal error: 'features.h' file not found
1 error generated.
#error Not a GNU libc system :-(
clang: error: linker command failed with exit code 1 (use -v to see invocation)
/* Override any gcc2 internal prototype to avoid an error.  */
clang: error: linker command failed with exit code 1 (use -v to see invocation)
configure:3516:10: fatal error: 'a.out.h' file not found
1 error generated.
configure:3516:10: fatal error: 'elf.h' file not found
1 error generated.
configure:3516:10: fatal error: 'cygwin/version.h' file not found
1 error generated.
configure:3516:10: fatal error: 'sys/pstat.h' file not found
1 error generated.
configure:3663:67: error: implicitly declaring library function 'exit' with type 'void (int) __attribute__((noreturn))' [-Werror,-Wimplicit-function-declaration]
1 error generated.
configure:4449:2: error: use of undeclared identifier 'not'
1 error generated.
configure:4519:11: error: implicitly declaring library function 'exit' with type 'void (int) __attribute__((noreturn))' [-Werror,-Wimplicit-function-declaration]
1 warning and 1 error generated.

I'm attaching the referenced log file.

[ryandesign (Ryan Carsten Schmidt)]

It is perfectly fine and accurate that features.h is not found. configure scripts test for the presence of various files and features to decide how to build on your system. Because it could not find features.h, it inferred that your system is not a GNU libc system, which is correct; macOS does not use glibc.

The real problem is that the writers of the configure script forgot to include essential headers, like those that define the exit() function, hence some later test fail unintentionally with error: implicitly declaring library function 'exit'. That's what needs to be fixed.

[wealthychef1]

Oh, another #include <unistd.h> thing I bet! Happened with compface yesterday.

[ryandesign (Ryan Carsten Schmidt)]

unistd.h does not define exit(); stdlib.h does. For each implicit declaration of function, it must be researched what the correct header is and the correct include must be added to the applicable code.

Duplicate of #61383.