autoconf: Checks for some programs

./configure script checks now for the following programs:
 * CC  - using AC_PROG_CC
 * AR  - using AC_CHECK_TOOL among ar
 * TAR - among gtar, tar

Checks not implemented:
 * INSTALL  - needs install-sh or install.sh in sources
 * RPMBUILD - not known alternatives for rpmbuild
 * PYTHON   - no PYTHON variable in Makefile,
              has to set NO_PYTHON if not present

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

config.mak.in

@@ -1,6 +1,11 @@
 # git Makefile configuration, included in main Makefile
 # @configure_input@
 
+CC = @CC@
+AR = @AR@
+TAR = @TAR@
+#INSTALL = @INSTALL@		# needs install-sh or install.sh in sources
+
 prefix = @prefix@
 exec_prefix = @exec_prefix@
 bindir = @bindir@

configure.ac

@@ -22,6 +22,13 @@ AC_DEFUN([GIT_CONF_APPEND_LINE],
 
 
 ## Checks for programs.
+AC_MSG_NOTICE([CHECKS for programs])
+
+AC_PROG_CC
+#AC_PROG_INSTALL		# needs install-sh or install.sh in sources
+AC_CHECK_TOOL(AR, ar, :)
+AC_CHECK_PROGS(TAR, [gtar tar])
+
 # Define NO_PYTHON if you want to loose all benefits of the recursive merge.