build: don't use make's -C; it's not available everywhere.

(Patch by Adrien Nader!)

-C doesn't work on at least openbsd's make so don't use it.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14173 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02

Makefile

@@ -19,7 +19,7 @@ CAMLC=$(CAMLC_BIN) -nostdlib -I boot
 CAMLOPT=$(CAMLOPT_BIN) -nostdlib -I stdlib -I otherlibs/dynlink
 COMPFLAGS=-strict-sequence -w +33..39 -warn-error A $(INCLUDES)
 LINKFLAGS=
-SWITCH_COMPILER=make -C $(ROOTDIR)/config -f Makefile.switch-compiler
+SWITCH_COMPILER=cd $(ROOTDIR)/config && $(MAKE) -f Makefile.switch-compiler
 
 CAMLYACC=boot/ocamlyacc
 YACCFLAGS=-v

configure

@@ -1741,7 +1741,7 @@ rm -f ../m.h ../s.h ../Makefile
 mv m.h s.h Makefile ..
 
 rm -f ../ocamlcomp
-make -C .. -f Makefile.switch-compiler disable COMPILER="CAMLC" VARIANT="BYTE"
+cd .. && make -f Makefile.switch-compiler disable COMPILER="CAMLC" VARIANT="BYTE"
 
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