autoconf: Subsitute SHELL for all platforms

Establish the shell that make will use from configure. This is exactly
how autoconf/automake operate, with the environment variable
CONFIG_SHELL respected to override the autoconf checks. In the usual
case where the user just executes `./configure', autoconf will pick a
shell from the current shell, sh, bash, ksh or sh5 that meets its base
criteria.

The special Solaris case of looking for a POSIX shell has been changed
to just set the SHELL variable since autoconf substitutes this already.
The EXTRA_CONFIG_LINES substitution is dropped as it should no longer be
needed.

configs/autoconf.in

@@ -27,6 +27,7 @@ ASM_API = @ASM_API@
 
 # Misc tools and flags
 MAKE = @MAKE@
+SHELL = @SHELL@
 MKLIB_OPTIONS = @MKLIB_OPTIONS@
 MKDEP = @MKDEP@
 MKDEP_OPTIONS = @MKDEP_OPTIONS@
@@ -101,6 +102,3 @@ DRI_DRIVER_INSTALL_DIR = @DRI_DRIVER_INSTALL_DIR@
 
 # Where libGL will look for DRI hardware drivers
 DRI_DRIVER_SEARCH_DIR = $(DRI_DRIVER_INSTALL_DIR)
-
-# Additional per-platform configuration settings
-@EXTRA_CONFIG_LINES@

configure.ac

@@ -33,18 +33,16 @@ AC_CHECK_PROGS([MAKE], [gmake make])
 AC_PATH_PROG([MKDEP], [makedepend])
 AC_PATH_PROG([SED], [sed])
 
-dnl Platform-specific program settings
-EXTRA_CONFIG_LINES=""
-AC_SUBST([EXTRA_CONFIG_LINES])
+dnl We need a POSIX shell for parts of the build. Assume we have one
+dnl in most cases.
 case "$host_os" in
 solaris*)
     # Solaris /bin/sh is too old/non-POSIX compliant
     AC_PATH_PROGS(POSIX_SHELL, [ksh93 ksh sh])
-    EXTRA_CONFIG_LINES="SHELL=$POSIX_SHELL"
+    SHELL="$POSIX_SHELL"
     ;;
 esac
 
-
 MKDEP_OPTIONS=-fdepend
 dnl Ask gcc where it's keeping its secret headers
 if test "x$GCC" = xyes; then