Apply suggestions from code review

Co-authored-by: Max Horn <max@quendi.de>

Author: vchuravy

src/staticdata.c

@@ -1251,7 +1251,7 @@ static void jl_write_values(jl_serializer_state *s) JL_GC_DISABLED
             write_uint8(s->s, '\0'); // null-terminated strings for easier C-compatibility
         }
         else if (jl_is_foreign_type(t) == 1) {
-            jl_error("Foreign Objects cannot be serialized");
+            jl_error("Cannot serialize instances of foreign datatypes");
         }
         else if (jl_datatype_nfields(t) == 0) {
             // The object has no fields, so we just snapshot its byte representation

test/gcext/Foreign/deps/foreignlib.c

@@ -18,8 +18,9 @@ void sweep(jl_value_t *p)
     nsweeps++;
 }
 
-JL_DLLEXPORT jl_datatype_t *declare_foreign(jl_sym_t* name, jl_module_t *module, jl_datatype_t *parent) {
-return jl_new_foreign_type(name, module, parent, mark, sweep, 1, 0);
+JL_DLLEXPORT jl_datatype_t *declare_foreign(jl_sym_t* name, jl_module_t *module, jl_datatype_t *parent)
+{
+     return jl_new_foreign_type(name, module, parent, mark, sweep, 1, 0);
 }
 
 // #define GC_MAX_SZCLASS (2032 - sizeof(void *))

test/gcext/Makefile

@@ -19,7 +19,12 @@ SRCDIR := $(abspath $(dir $(lastword $(MAKEFILE_LIST))))
 # get the executable suffix, if any
 EXE := $(suffix $(abspath $(JULIA)))
 
-DYLIB := .so
+OS := $(shell uname)
+ifeq ($(OS), Darwin)
+  DYLIB := .dylib
+else
+  DYLIB := .so
+endif
 
 # get compiler and linker flags. (see: `contrib/julia-config.jl`)
 JULIA_CONFIG := $(JULIA) -e 'include(joinpath(Sys.BINDIR, Base.DATAROOTDIR, "julia", "julia-config.jl"))' --