bug#45164: FYI, I've just pushed some small build changes

[Jim Meyering]

commit 01458f8fdb21bcceaf41b2c18ff45817e13183e1 (HEAD -> master)
Author: Jim Meyering <meyering@fb.com>
Date:   Wed Dec 9 20:55:20 2020 -0800

    maint: avoid another autoreconf warning

    * configure.ac: modernize AC_TRY_COMPILE invocation
    Use AC_COMPILE_IFELSE instead of AC_TRY_COMPILE.

commit fb973ec75a15e0379a31fd9fa99ad64d0c8396c1
Author: Jim Meyering <meyering@fb.com>
Date:   Wed Dec 9 20:40:29 2020 -0800

    maint: remove uses of obsolete macros

    * configure.ac (AC_TYPE_SIGNAL, AC_ISC_POSIX, AC_HEADER_STDC): Remove.

commit 598fbc23964e1d991526c4fb8687a0b0fda95bd2
Author: Jim Meyering <meyering@fb.com>
Date:   Wed Dec 9 20:38:36 2020 -0800

    maint: avoid autoreconf warnings

    * configure.ac: Go back to using AC_PROG_CC rather than AC_PROG_CC_STDC,
    as the latter is obsolescent and the Autoconf bug involving the former
    has been fixed.

commit 73f84324be73d3e002c36fbe2f9a67c717fbf09b
Author: Jim Meyering <meyering@fb.com>
Date:   Wed Dec 9 20:29:03 2020 -0800

    build: update gnulib to latest