gnu: ocaml@4.07: Fix link failure.

The link failure shows up when using ld from GNU Binutils 2.37, and not
with 2.34.

* gnu/packages/patches/ocaml-multiple-definitions.patch: New file.
* gnu/packages/ocaml.scm (ocaml-4.07-boot)[source]: Use it.
* gnu/local.mk (dist_patch_DATA): Add it.

gnu/local.mk

@@ -1485,6 +1485,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/ocaml-dose3-Fix-for-ocaml-4.06.patch	\
   %D%/packages/patches/ocaml-dose3-dont-make-printconf.patch	\
   %D%/packages/patches/ocaml-dose3-Install-mli-cmx-etc.patch	\
+  %D%/packages/patches/ocaml-multiple-definitions.patch		\
   %D%/packages/patches/omake-fix-non-determinism.patch	\
   %D%/packages/patches/oneko-remove-nonfree-characters.patch	\
   %D%/packages/patches/onnx-use-system-googletest.patch	\

gnu/packages/ocaml.scm

@@ -275,6 +275,7 @@ functional, imperative and object-oriented styles of programming.")
               (sha256
                (base32
                 "1f07hgj5k45cylj1q3k5mk8yi02cwzx849b1fwnwia8xlcfqpr6z"))
+              (patches (search-patches "ocaml-multiple-definitions.patch"))
               (modules '((guix build utils)))
               (snippet
                `(begin

gnu/packages/patches/ocaml-multiple-definitions.patch

@@ -0,0 +1,43 @@
+Avoid multiply-defined symbols that lead to link errors such as:
+
+  gcc -O2 -fno-strict-aliasing -fwrapv -Wall -fno-tree-vrp  -g -D_FILE_OFFSET_BITS=64 -D_REENTRANT -DCAML_NAME_SPACE  -Wl,-E -o ocamlruni prims.o libcamlruni.a -lm  -ldl -lpthread 
+  ld: libcamlruni.a(backtrace.i.o):/tmp/guix-build-ocaml-4.07.1.drv-0/ocaml-4.07.1/byterun/backtrace.c:31: multiple definition of `caml_debug_info'; libcamlruni.a(backtrace_prim.i.o):/tmp/guix-build-ocaml-4.07.1.drv-0/ocaml-4.07.1/byterun/backtrace_prim.c:47: first defined here
+
+diff --git a/asmrun/startup.c b/asmrun/startup.c
+index 070f0c6..cf8a56f 100644
+--- a/asmrun/startup.c
++++ b/asmrun/startup.c
+@@ -44,7 +44,6 @@
+ #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;
+ 
+diff --git a/byterun/backtrace.c b/byterun/backtrace.c
+index 8dfe9b7..9cc9e72 100644
+--- a/byterun/backtrace.c
++++ b/byterun/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/byterun/backtrace_prim.c b/byterun/backtrace_prim.c
+index e69b256..d794f73 100644
+--- a/byterun/backtrace_prim.c
++++ b/byterun/backtrace_prim.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;
+