dnl
dnl https://github.com/pkgconf/pkgconf/blob/master/pkg.m4#L217-L236
dnl
dnl PKG_INSTALLDIR([DIRECTORY])
dnl -------------------------
dnl Since: 0.27
dnl
dnl Substitutes the variable pkgconfigdir as the location where a module
dnl should install pkg-config .pc files. By default the directory is
dnl $libdir/pkgconfig, but the default can be changed by passing
dnl DIRECTORY. The user can override through the --with-pkgconfigdir
dnl parameter.
AC_DEFUN([PKG_INSTALLDIR],
[m4_pushdef([pkg_default], [m4_default([$1], ['${libdir}/pkgconfig'])])
m4_pushdef([pkg_description],
    [pkg-config installation directory @<:@]pkg_default[@:>@])
AC_ARG_WITH([pkgconfigdir],
    [AS_HELP_STRING([--with-pkgconfigdir], pkg_description)],,
    [with_pkgconfigdir=]pkg_default)
AC_SUBST([pkgconfigdir], [$with_pkgconfigdir])
m4_popdef([pkg_default])
m4_popdef([pkg_description])
])dnl PKG_INSTALLDIR