Export C/C++ compiler found in Cxx_flags

Signed-off-by: Antonin Décimo <antonin@tarides.com>

src/dune_rules/cxx_flags.ml

@@ -42,4 +42,4 @@ let get_flags dir =
   let open Build.O in
   let+ ccomp_type = ccomp_type dir in
   check_warn ccomp_type;
-  base_cxx_flags ccomp_type
+  (ccomp_type, base_cxx_flags ccomp_type)

src/dune_rules/cxx_flags.mli

@@ -4,10 +4,17 @@ open! Stdune
 
 open Dune_engine
 
+(** The detected compiler *)
+type ccomp_type =
+  | Gcc
+  | Msvc
+  | Clang
+  | Other of string
+
 (** The name of the file created in the .dune folder after calling the C
     preprocessor *)
 val preprocessed_filename : string
 
 (** [get_flags c_compiler] returns the necessary flags to turn this compiler
     into a c++ compiler for some of the most common compilers *)
-val get_flags : Path.Build.t -> string list Build.t
+val get_flags : Path.Build.t -> (ccomp_type * string list) Build.t

src/dune_rules/super_context.ml

@@ -16,7 +16,7 @@ let default_context_flags (ctx : Context.t) ~project =
       let c = cflags @ Ocaml_config.ocamlc_cppflags ctx.ocaml_config in
       let cxx =
         let open Build.O in
-        let+ db_flags = Cxx_flags.get_flags ctx.build_dir in
+        let+ _, db_flags = Cxx_flags.get_flags ctx.build_dir in
         db_flags @ cxxflags
       in
       (Build.return c, cxx)