Support more special chars in $(LIBDIR) etc

* lib/autoconf/libs.m4 (_AC_PATH_X_XMKMF):
* lib/autoconf/programs.m4 (AC_PROG_MAKE_SET):
Allow more special characters in ‘make’ macros like LIBDIR and MAKE.

lib/autoconf/libs.m4

@@ -170,11 +170,11 @@ if mkdir conftest.dir; then
   cd conftest.dir
   cat >Imakefile <<'_ACEOF'
 incroot:
-	@echo incroot='${INCROOT}'
+	@printf '%s\n' incroot='${INCROOT}'
 usrlibdir:
-	@echo usrlibdir='${USRLIBDIR}'
+	@printf '%s\n' usrlibdir='${USRLIBDIR}'
 libdir:
-	@echo libdir='${LIBDIR}'
+	@printf '%s\n' libdir='${LIBDIR}'
 _ACEOF
   if (export CC; ${XMKMF-xmkmf}) >/dev/null 2>/dev/null && test -f Makefile; then
     # GNU make sometimes prints "make[1]: Entering ...", which would confuse us.

lib/autoconf/programs.m4

@@ -936,7 +936,7 @@ AC_CACHE_VAL(ac_cv_prog_make_${ac_make}_set,
 [cat >conftest.make <<\_ACEOF
 SHELL = /bin/sh
 all:
-	@echo '@@@%%%=$(MAKE)=@@@%%%'
+	@printf '%s\n' '@@@%%%=$(MAKE)=@@@%%%'
 _ACEOF
 # GNU make sometimes prints "make[1]: Entering ...", which would confuse us.
 case `${MAKE-make} -f conftest.make 2>/dev/null` in