Changes

Typo in stdlib/Makefile

Affects forced recompilation of runtime-launch-info

Reduce tmpheader.exe to 4-5KiB on Windows

stdlib/headernt.c was adapted in OCaml 3.00 to reduce its size by
avoiding the use of the CRT and using Windows API functions directly
(this is a well-studied trick on Windows, principally as a puzzle for
producing tiny binaries).

This got "regressed" slightly in OCaml 4.06, in the complex introduction
of wide character support for Windows, as the mingw-w64 incantation
required was unclear, so the entry point was changed to wmain, and the
size of the header increased.

By switching from wcslen (a CRT function) to lstrlen (a Win32 API
function), headernt.c again only requires kernel32.dll.

Additional flags are added for both ld (mingw-w64) and link (MSVC) to
squeeze every last byte out of tmpheader.exe. The MSVC version of the
header is once again no longer passed through strip, as this was found
to be corrupting the executable (and had never been reducing its size
anyway).

Stop using Caml_inline and CAMLnoret in headernt.c

Modern C compilers are sufficiently intelligent not to need the inlining
hints!

Inline the definition from caml/misc.h for CAMLnoret.

Co-authored-by: Antonin Décimo <antonin@tarides.com>

Remove unnecessary guards around unistd.h

Already updated to remove the actual test in s.h, since XPG1 (1985)
required it and it is therefore part of the Single Unix
Specification (1992), but the _WIN32 guard and the loading of s.h are
unnecessary.

Use PATH_MAX instead of MAXPATHLEN

Assume S_ISREG and SEEK_END

Defined in sys/stat.h and unistd.h respectively by the Single Unix
Specification.

Move O_BINARY definition to "header" section

O_BINARY is added for maximum Cygwin compatibility, but it's not a Posix
flag.

Make caml/exec.h independent

Have exec.h include <stdint.h> itself. The bytecode executable header
now only depends on exec.h.

Re-order some header functions (no-op)

Share error path in headernt.c

Unify implementation of read_size

Modernisations applied in headernt.c but not applied to header.c - use
uint32_t rather than unsigned long

headernt.c: inline run_runtime into main

Check for errors from lseek in header.c

Refactor error display code

header.c: close bytecode image before exec

Leaking fd

Use execvp in header.c (as in headernt.c)

Brings the behaviour of the two headers into line with each other - if
RNTM is ocamlrun on Unix, ocamlrun will now be sought in PATH.

headernt: make read_runtime_path more CRTish

Missing error case in headernt.c

Unify the common parts of header.c and headernt.c

Merge stdlib/header{,nt}.c