MPR#7679: make sure `.a` files are erased before calling `ar rc` (#1494)

Otherwise leftover .a files from an earlier compilation may contain
unwanted modules, as shown in MPR#7679.

However, ocamlmklib always erases the destination .a file before
calling the `mkdll` function defined in `#ml` blocks of the
configuration makefile.  Hence there is no need for a `rm` (or `del`)
shell command in `mklib`.

Finally, in the config/Makefile.mingw* files, we can safely assume
"ar" supports the "s" option because this is "ar" from the GNU
binutils, so no need to call ranlib.

Changes

@@ -58,6 +58,10 @@ Working version
 
 ### Compiler distribution build system
 
+- MPR#7679: make sure .a files are erased before calling ar rc, otherwise
+  leftover .a files from an earlier compilation may contain unwanted modules
+  (Xavier Leroy)
+
 ### Internal/compiler-libs changes:
 
 ### Bug fixes

config/Makefile.mingw

@@ -156,10 +156,10 @@ MKEXE_BOOT=$(CC) $(CFLAGS) $(LDFLAGS) $(OUTPUTEXE)$(1) $(2)
 MKEXE_ANSI=$(FLEXLINK) -exe
 
 ### How to build a static library
-MKLIB=rm -f $(1); $(TOOLPREF)ar rc $(1) $(2); $(RANLIB) $(1)
+MKLIB=rm -f $(1) && $(TOOLPREF)ar rcs $(1) $(2)
 #ml let mklib out files opts =
-#ml   Printf.sprintf "rm -f %s && %sar rcs %s %s %s"
-#ml                  out toolpref opts out files;;
+#ml   Printf.sprintf "%sar rcs %s %s %s"
+#ml                  toolpref opts out files;;
 
 ### Canonicalize the name of a system library
 SYSLIB=-l$(1)

config/Makefile.mingw64

@@ -156,10 +156,10 @@ MKEXE_BOOT=$(CC) $(CFLAGS) $(LDFLAGS) $(OUTPUTEXE)$(1) $(2)
 MKEXE_ANSI=$(FLEXLINK) -exe
 
 ### How to build a static library
-MKLIB=rm -f $(1); $(TOOLPREF)ar rc $(1) $(2); $(RANLIB) $(1)
+MKLIB=rm -f $(1) && $(TOOLPREF)ar rcs $(1) $(2)
 #ml let mklib out files opts =
-#ml   Printf.sprintf "rm -f %s && %sar rcs %s %s %s"
-#ml                  out toolpref opts out files;;
+#ml   Printf.sprintf "%sar rcs %s %s %s"
+#ml                  toolpref opts out files;;
 
 ### Canonicalize the name of a system library
 SYSLIB=-l$(1)

configure

@@ -2057,9 +2057,9 @@ SYSLIB=-l\$(1)
 #ml let syslib x = "-l"^x;;
 
 ### How to build a static library
-MKLIB=${TOOLPREF}ar rc \$(1) \$(2); ${TOOLPREF}ranlib \$(1)
+MKLIB=rm -f \$(1) && ${TOOLPREF}ar rc \$(1) \$(2) && ${TOOLPREF}ranlib \$(1)
 #ml let mklib out files opts =      (* "" *)
-#ml   Printf.sprintf "${TOOLPREF}ar rc %s %s %s; ${TOOLPREF}ranlib %s"
+#ml   Printf.sprintf "${TOOLPREF}ar rc %s %s %s && ${TOOLPREF}ranlib %s"
 #ml                  out opts files out;;
 EOF
 config ARCH "$arch"