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;
 
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<div class='path'>path: <a href='/guix/log/?id=9834d1ab3836730cf3308603019b736d0a653013'>root</a>/<a href='/guix/log/gnu?id=9834d1ab3836730cf3308603019b736d0a653013'>gnu</a>/<a href='/guix/log/gnu/packages?id=9834d1ab3836730cf3308603019b736d0a653013'>packages</a>/<a href='/guix/log/gnu/packages/php.scm?id=9834d1ab3836730cf3308603019b736d0a653013'>php.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/php.scm?id=9834d1ab3836730cf3308603019b736d0a653013&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-11-26 04:22:51 +0100'>2020-11-26</span></td><td><a href='/guix/commit/gnu/packages/php.scm?id=824a9f1060111d9ab2317b1453360e39eda8201a'>gnu: php: Update to 7.4.13.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/php.scm (php): Update to 7.4.13.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-11-05 03:46:09 +0100'>2020-11-05</span></td><td><a href='/guix/commit/gnu/packages/php.scm?id=08d8e76678c7cedb65f2faded6310f140f31164e'>gnu: php: Move a test disablement.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/php.scm (php)[arguments]: Disable bug73837.phpt under a
more appropriate comment section.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-10-30 09:51:38 +0100'>2020-10-30</span></td><td><a href='/guix/commit/gnu/packages/php.scm?id=697d2e037bc999760b85b7904079679e0ccc1e62'>gnu: php: Update to 7.4.12 [security fixes].</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/php.scm (php): Update to 7.4.12.
[arguments]: Disable two more failing tests.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-10-01 00:13:41 +0200'>2020-10-01</span></td><td><a href='/guix/commit/gnu/packages/php.scm?id=9e93bffb58b3992bdcf5a0a2dc9f5bc9cd1cffd5'>gnu: php: Update to 7.4.11.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/php.scm (php): Update to 7.4.11.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-09-21 15:24:07 +0200'>2020-09-21</span></td><td><a href='/guix/commit/gnu/packages/php.scm?id=f23e439f9f89b8dbcc5bf76135842a1e49f8526a'>gnu: php: Disable unreliable test.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/php.scm (php)[arguments]: Delete bug73837.phpt.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-09-04 11:01:04 +0200'>2020-09-04</span></td><td><a href='/guix/commit/gnu/packages/php.scm?id=eb3328004ebf69d258b1afc46b5cab010c1a4a26'>gnu: php: Update to 7.4.10.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/php.scm (php): Update to 7.4.10.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-08-13 16:09:40 +0200'>2020-08-13</span></td><td><a href='/guix/commit/gnu/packages/php.scm?id=d1c37def6e22fa4e171a96f97347220cf2ed5aa9'>gnu: php: Update to 7.4.9.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/php.scm (php): Update to 7.4.9.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-07-11 23:24:29 +0200'>2020-07-11</span></td><td><a href='/guix/commit/gnu/packages/php.scm?id=7ed0eeb0113f4fe7c56ca649c05b08df8ecd66fb'>gnu: php: Update to 7.4.8.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/php.scm (php): Update to 7.4.8.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>