feat(link): drive output names and link flags from the object format

lib/binfmt.ml

@@ -0,0 +1,43 @@
+(* Output naming and linker flags follow the object file format, not the
+   operating system: the same triple can name a platform whose format decides
+   whether a shared library carries a lib prefix, needs an import library, or
+   has any notion of a soname at all. *)
+type t = Elf | Macho | Coff | Wasm
+
+let of_platform = function
+  | "darwin" -> Macho
+  | "windows" -> Coff
+  | "wasm" -> Wasm
+  | _ -> Elf
+
+let name = function Elf -> "elf" | Macho -> "macho" | Coff -> "coff" | Wasm -> "wasm"
+let exe_ext = function Coff -> ".exe" | Wasm -> ".wasm" | Elf | Macho -> ""
+
+(* Archives are written by ar and read back through -l, so they are named the
+   same way everywhere, including for the gnu ABI on Windows. *)
+let static_name n = "lib" ^ n ^ ".a"
+
+(* COFF keeps the plain name and links through a separate import library, while
+   the other formats carry the prefix in the shared object name itself. *)
+let shared_name fmt n =
+  match fmt with
+  | Elf -> "lib" ^ n ^ ".so"
+  | Macho -> "lib" ^ n ^ ".dylib"
+  | Coff -> n ^ ".dll"
+  | Wasm -> "lib" ^ n ^ ".wasm"
+
+let import_name fmt n = match fmt with Coff -> Some ("lib" ^ n ^ ".dll.a") | _ -> None
+
+(* COFF and wasm are position independent by construction, and their drivers
+   warn about a flag that cannot mean anything to them. *)
+let pic_flags = function Elf | Macho -> [ "-fPIC" ] | Coff | Wasm -> []
+let shared_flags = function Macho -> [ "-dynamiclib" ] | Elf | Coff | Wasm -> [ "-shared" ]
+
+let soname_flags fmt s =
+  match fmt with
+  | Elf -> [ "-Wl,-soname," ^ s ]
+  | Macho -> [ "-Wl,-install_name," ^ s ]
+  | Coff | Wasm -> []
+
+let implib_flags fmt path =
+  match fmt with Coff -> [ "-Wl,--out-implib," ^ path ] | Elf | Macho | Wasm -> []