aclocal.m4: Update PKG_* macros to pkg-config 0.29.2

aclocal.m4: Update PKG_* macros to pkg-config 0.29.2

This commit removes the old definition of PKG_CHECK_MODULES (from 2004) and
simply appends a recent version of pkg-config's file `pkg.m4` at the end of
`aclocal.m4`.

This immediately improves documentation of pkg-config stuff.  Now the list
of environment variables shown in `configure --help` ends with

  PKG_CONFIG  path to pkg-config utility
  PKG_CONFIG_PATH
              directories to add to pkg-config's search path
  PKG_CONFIG_LIBDIR
              path overriding pkg-config's built-in search path
  GUILE_CFLAGS
              C compiler flags for GUILE, overriding pkg-config
  GUILE_LIBS  linker flags for GUILE, overriding pkg-config
  BDWGC_CFLAGS
              C compiler flags for BDWGC, overriding pkg-config
  BDWGC_LIBS  linker flags for BDWGC, overriding pkg-config
  PANGO_FT2_CFLAGS
              C compiler flags for PANGO_FT2, overriding pkg-config
  PANGO_FT2_LIBS
              linker flags for PANGO_FT2, overriding pkg-config
  FONTCONFIG_CFLAGS
              C compiler flags for FONTCONFIG, overriding pkg-config
  FONTCONFIG_LIBS
              linker flags for FONTCONFIG, overriding pkg-config
  FREETYPE2_CFLAGS
              C compiler flags for FREETYPE2, overriding pkg-config
  FREETYPE2_LIBS
              linker flags for FREETYPE2, overriding pkg-config
  GLIB_CFLAGS C compiler flags for GLIB, overriding pkg-config
  GLIB_LIBS   linker flags for GLIB, overriding pkg-config
  GOBJECT_CFLAGS
              C compiler flags for GOBJECT, overriding pkg-config
  GOBJECT_LIBS
              linker flags for GOBJECT, overriding pkg-config

[hanwenn, 2020-03-07 09:32:47]

https://codereview.appspot.com/551590044/diff/553640043/aclocal.m4
File aclocal.m4 (right):

https://codereview.appspot.com/551590044/diff/553640043/aclocal.m4#newcode1127
aclocal.m4:1127: # pkg.m4 - Macros to locate and utilise pkg-config.   -*-
Autoconf -*-
can we include this rather than copy & paste?

[hahnjo, 2020-03-07 09:36:25]

The update LGTM

On 2020/03/07 09:32:47, hanwenn wrote:
> https://codereview.appspot.com/551590044/diff/553640043/aclocal.m4
> File aclocal.m4 (right):
> 
> https://codereview.appspot.com/551590044/diff/553640043/aclocal.m4#newcode1127
> aclocal.m4:1127: # pkg.m4 - Macros to locate and utilise pkg-config.   -*-
> Autoconf -*-
> can we include this rather than copy & paste?

This would require generating aclocal.m4 by aclocal as part of generating
configure. I'm all for doing this, but I'd avoid doing this level of tooling
changes before 2.21.0

[lemzwerg, 2020-03-07 09:46:48]

> > can we include this rather than copy & paste?
> 
> This would require generating aclocal.m4 by aclocal as 
> part of generating configure. I'm all for doing this,
> but I'd avoid doing this level of tooling changes
> before 2.21.0

Seconded.

[lemzwerg, 2020-03-07 14:11:18]

rebase