Install pkg-config link with $host- prefix

If pkg-config is used in a multiarch or cross-compiling scenario it's
likely pkg-config needs to behave differently for each of them. It's
possible to handle this through environment variables with one
pkg-config, but another option is to have one pkg-config per platform,
each with the host alias prefixed to the program.

PKG_PROG_PKG_CONFIG supports this type of installation, and this is also
how autoconf/libtool handle other build tools like compilers and
linkers.

The host-prefixed tool is installed as a hardlink where supported and a
copy otherwise. This is how gcc handles it's host-prefixed versions.
This feature can be turned off by passing --disable-host-tool to
configure.

Freedesktop #130

Makefile.am

@@ -36,6 +36,12 @@ pkg_config_SOURCES= \
 	parse.c \
 	main.c
 
+if HOST_TOOL
+host_tool = $(host)-pkg-config$(EXEEXT)
+install-exec-hook:
+	cd $(DESTDIR)$(bindir) && $(LN) pkg-config$(EXEEXT) $(host_tool)
+endif
+
 # Various data files
 m4dir = $(datadir)/aclocal
 dist_m4_DATA = pkg.m4

configure.ac

@@ -19,6 +19,7 @@ m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])])
 
 dnl Check for programs
 AC_PROG_CC
+AC_CHECK_PROG([LN], [ln], [ln], [cp -Rp])
 
 dnl Check for headers
 AC_CHECK_HEADERS([dirent.h unistd.h sys/wait.h malloc.h])
@@ -203,6 +204,18 @@ if test "x$with_gcov" = xyes; then
 fi
 AC_SUBST([GCOV_CFLAGS])
 
+dnl See if the user wants a host- prefixed tool
+dnl (e.g. i686-pc-linux-gnu-pkg-config) to be installed.
+dnl
+AC_MSG_CHECKING([if host- prefixed tool should be installed])
+AC_ARG_ENABLE([host-tool],
+  [AS_HELP_STRING([--disable-host-tool],
+    [install link to pkg-config with $host- prefix @<:@default=yes@:>@])],
+  [],
+  [enable_host_tool=yes])
+AC_MSG_RESULT([$enable_host_tool])
+AM_CONDITIONAL([HOST_TOOL], [test "x$enable_host_tool" = xyes])
+
 AC_CONFIG_FILES([
 Makefile
 check/Makefile