Use :standard in dune flags stanza

[PerfectLaugh]

The include flag causes compilation error on OCaml 5.4.0 and gcc (GCC) 15.2.1 20251022 (Red Hat 15.2.1-3)

Log:

File "src/dune", lines 1-8, characters 0-162:
1 | (library
2 |  (name bitstring)
3 |  (public_name bitstring)
4 |  (foreign_stubs
5 |   (language c)
6 |   (names bitstring_fastpath)
7 |   (flags -I.))
8 |  (libraries str unix stdlib-shims))
/usr/bin/ld: src/bitstring_fastpath.o: relocation R_X86_64_32S against
`.data' can not be used when making a shared object; recompile with
-fPIC
/usr/bin/ld: failed to set dynamic section sizes: bad value
collect2: error: ld returned 1 exit status

[xguerin]

This PR looks fine. However, I fail to see how an include path can cause the linker to fail. I'm gonna check your setup on my end to see what's going on.

[PerfectLaugh]

I build on Fedora 43 x86_64. Either adding -fPIC in flags or remove the flags stanza will work.
But I suggest remove the flags completely to comply with possible standard flags in OCaml

[xguerin]

Would adding :standard help here? (cflags :standard -I.). I'm thinking -fPIC may be added in a target-specific manner and present in the default flags.

[PerfectLaugh]

Would adding :standard help here? (cflags :standard -I.). I'm thinking -fPIC may be added in a target-specific manner and present in the default flags.

Sounds great. I didn't know the :standard flag before, it should be preferred.