Make ocamlc and optional dependency.

Since moving to a downloadable snapshot for stage0, it's been
possible to complete the build without compiling code written
in ocaml. However, the configure script still required it to
be present.

This commit changes detection failure to a non-fatal condition,
allowing the build to complete on systems without an ocaml
compiler.

An info message is also made conditional.

Author: rillian

Diff for: Makefile.in

@@ -38,7 +38,7 @@ CFG_STDLIB :=$(call CFG_LIB_NAME,std)
 ifdef CFG_OCAMLC_OPT
   $(info cfg: have ocaml native compiler)
   OPT=.opt
-else
+else ifdef CFG_OCAMLC
   $(info cfg: have only ocaml bytecode compiler)
 endif
 

Diff for: configure

@@ -186,13 +186,13 @@ putvar CFG_CONFIGURE_ARGS
 step_msg "looking for build programs"
 probe_need CFG_GCC          gcc
 probe_need CFG_GIT          git
-probe_need CFG_OCAMLC       ocamlc
 probe_need CFG_PERL         perl
 probe_need CFG_PYTHON       python
 probe_need CFG_CURL         curl
 
 probe CFG_LLVM_CONFIG      llvm-config
 probe CFG_VALGRIND         valgrind
+probe CFG_OCAMLC           ocamlc
 probe CFG_OCAMLOPT         ocamlopt
 probe CFG_OCAMLC_OPT       ocamlc.opt
 probe CFG_OCAMLOPT_OPT     ocamlopt.opt