Add missing include that triggers a build failure on PowerPC:

  ../../../../gcc-5.4.0/libsanitizer/asan/asan_linux.cc: In function ‘bool __asan::AsanInterceptsSignal(int)’:
  ../../../../gcc-5.4.0/libsanitizer/asan/asan_linux.cc:222:20: error: ‘SIGSEGV’ was not declared in this scope
     return signum == SIGSEGV && common_flags()->handle_segv;
		      ^
From <https://patchwork.ozlabs.org/patch/725596/>.

diff --git a/libsanitizer/asan/asan_linux.cc b/libsanitizer/asan/asan_linux.cc
index c504168..59087b9 100644
--- a/libsanitizer/asan/asan_linux.cc
+++ b/libsanitizer/asan/asan_linux.cc
@@ -29,6 +29,7 @@
 #include <dlfcn.h>
 #include <fcntl.h>
 #include <pthread.h>
+#include <signal.h>
 #include <stdio.h>
 #include <unistd.h>
 #include <unwind.h>
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<tr><td><span title='2022-11-24 08:48:31 +0200'>2022-11-24</span></td><td><a href='/guix/commit/gnu/packages/gawk.scm?id=ee9bf36b8d901f470e46b283801dbe1e8d6d6615'>gnu: gawk: Update to 5.2.1.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2022-09-08 21:39:59 +0200'>2022-09-08</span></td><td><a href='/guix/commit/gnu/packages/gawk.scm?id=845bc594023e22fe1994afde29e2c3c4ae4343b9'>gnu: gawk: Update to 5.2.0.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2022-07-22 01:09:14 +0200'>2022-07-22</span></td><td><a href='/guix/commit/gnu/packages/gawk.scm?id=9044b086ddca64a62966a83cbf1b82d32dece89e'>Merge branch 'staging' into core-updates</a></td><td>Marius Bakke</td></tr>
<tr><td><span title='2022-07-08 17:36:51 +0200'>2022-07-08</span></td><td><a href='/guix/commit/gnu/packages/gawk.scm?id=e07fa9b04009f0b239931674e1a48536a52e3276'>gnu: Add cppawk and cppawk-egawk.</a><span class='msg-avail'>...</span></td><td>Paul A. Patience</td></tr>
<tr><td><span title='2022-07-08 17:36:38 +0200'>2022-07-08</span></td><td><a href='/guix/commit/gnu/packages/gawk.scm?id=1fed71ce1976db9edf95fc4b99cac75a281fb526'>gnu: Add egawk-next.</a><span class='msg-avail'>...</span></td><td>Paul A. Patience</td></tr>
<tr><td><span title='2022-07-08 17:36:27 +0200'>2022-07-08</span></td><td><a href='/guix/commit/gnu/packages/gawk.scm?id=2e5c519b3f5d12b41132d535164fa04801f1bd4e'>gnu: Add gawk-mpfr.</a><span class='msg-avail'>...</span></td><td>Paul A. Patience</td></tr>
<tr><td><span title='2022-07-08 17:36:23 +0200'>2022-07-08</span></td><td><a href='/guix/commit/gnu/packages/gawk.scm?id=f5efde47f7d21f1f35f8b974af8d8f375114a6ea'>gnu: Use 'license:' prefix in (gnu packages gawk).</a><span class='msg-avail'>...</span></td><td>Paul A. Patience</td></tr>
<tr><td><span title='2022-06-26 22:58:33 +0200'>2022-06-26</span></td><td><a href='/guix/commit/gnu/packages/gawk.scm?id=da25a43f2dc582249f50d67119ea894c216db048'>gnu: gawk: Use G-expressions and remove labels.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2022-06-26 22:58:33 +0200'>2022-06-26</span></td><td><a href='/guix/commit/gnu/packages/gawk.scm?id=003128f2f3e499b5064679a3ad4b63d911f3b777'>gnu: gawk: Update to 5.1.1.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>