ocamltest: Makefile improvements

- Use := everywhere
- Merge two ifeq blocks

ocamltest/Makefile

@@ -21,9 +21,15 @@ ifeq "$(UNIX_OR_WIN32)" "win32"
   unix := false
   ocamlsrcdir := $(shell echo "$(abspath $(shell pwd)/..)"|cygpath -w -f - \
     | sed 's/\\/\\\\\\\\/g')
+  ifeq "$(wildcard ../flexdll/Makefile)" ""
+    FLEXLINK_ENV=
+  else
+    FLEXLINK_ENV=OCAML_FLEXLINK="../boot/ocamlrun ../flexdll/flexlink.exe"
+  endif
 else
   unix := true
   ocamlsrcdir := $(abspath $(shell pwd)/..)
+  FLEXLINK_ENV=
 endif
 
 ifeq "$(TOOLCHAIN)" "msvc"
@@ -119,24 +125,14 @@ bytecode_modules := $(o_files) $(cmo_files)
 
 native_modules := $(o_files) $(cmx_files)
 
-directories = ../utils ../parsing ../stdlib ../compilerlibs
+directories := ../utils ../parsing ../stdlib ../compilerlibs
 
-include_directories = $(addprefix -I , $(directories))
+include_directories := $(addprefix -I , $(directories))
 
-flags = -g -nostdlib $(include_directories) \
+flags := -g -nostdlib $(include_directories) \
   -strict-sequence -safe-string -strict-formats \
   -w +a-4-9-41-42-44-45-48 -warn-error A
 
-ifeq "$(UNIX_OR_WIN32)" "unix"
-FLEXLINK_ENV=
-else # Windows
-  ifeq "$(wildcard ../flexdll/Makefile)" ""
-    FLEXLINK_ENV=
-  else
-    FLEXLINK_ENV=OCAML_FLEXLINK="../boot/ocamlrun ../flexdll/flexlink.exe"
-  endif
-endif
-
 ocamlc := $(FLEXLINK_ENV) ../byterun/ocamlrun ../ocamlc $(flags)
 
 ocamlopt := $(FLEXLINK_ENV) ../byterun/ocamlrun ../ocamlopt $(flags)