Avoid multiply-defined symbols that lead to link errors such as:

  ld: libcamlrund.a(backtrace_bd.o):/tmp/guix-build-ocaml-4.09.0.drv-0/ocaml-4.09.0/runtime/backtrace.c:31: multiple definition of `caml_debug_info'; libcamlrund.a(backtrace_byt_bd.o):/tmp/guix-build-ocaml-4.09.0.drv-0/ocaml-4.09.0/runtime/backtrace_byt.c:47: first defined here

diff --git a/runtime/backtrace.c b/runtime/backtrace.c
index a3c2c08..f57c81c 100644
--- a/runtime/backtrace.c
+++ b/runtime/backtrace.c
@@ -28,7 +28,7 @@
 #include "caml/fail.h"
 
 /* The table of debug information fragments */
-struct ext_table caml_debug_info;
+static struct ext_table caml_debug_info;
 
 CAMLexport int32_t caml_backtrace_active = 0;
 CAMLexport int32_t caml_backtrace_pos = 0;
diff --git a/runtime/backtrace_byt.c b/runtime/backtrace_byt.c
index b913dac..b5ec926 100644
--- a/runtime/backtrace_byt.c
+++ b/runtime/backtrace_byt.c
@@ -44,7 +44,7 @@
 #include "caml/backtrace_prim.h"
 
 /* The table of debug information fragments */
-struct ext_table caml_debug_info;
+static struct ext_table caml_debug_info;
 
 CAMLexport char_os * caml_cds_file = NULL;
 
diff --git a/runtime/startup_nat.c b/runtime/startup_nat.c
index b4e6bc4..7eca5fa 100644
--- a/runtime/startup_nat.c
+++ b/runtime/startup_nat.c
@@ -44,6 +44,5 @@
 #endif
 
 extern int caml_parser_trace;
-CAMLexport header_t caml_atom_table[256];
 char * caml_code_area_start, * caml_code_area_end;
 struct ext_table caml_code_fragments_table;