RFC: Changing AC_PROG_CC to AC_PROG_CC_C99 in top level configure

[Simon Marchi]

On 2021-05-03 5:51 p.m., Alan Modra wrote:
> I wasn't talking about running configure, I was talking about running
> make.  For example, you configure and make binutils as usual, then
> after making a change to ld/ files, run make in the ld build dir.  I
> don't tend to do that myself but I do run "make check" sometimes in a
> subdir expecting to get the same results in that subdir as if "make
> check" was run from the top level.

Ah yeah, that works just fine.  During my edit-build-cycle, I typically
only "make" in gdb/, or whatever I'm working on at the moment.  It saves
some precious milliseconds!

> But I should have just tried it myself rather than asking.  CC, CPP
> and others are inherited from the top level and appear with -std=gnu99
> in the subdir Makefiles.  So it seems all the AC_PROG_CC in subdir
> configure.ac can stay as they are.

Yes, the top-level passes CC=... and others when it configures the
subdirectories.  The subdirectories remember how they were configures
(in config.status), so that even if a "make" in the subdirectory ends up
re-running configure (because configure changed), the CC value will be
remembered.

Simon