Fix esan compilation against glibc 2.26:

  /tmp/guix-build-clang-runtime-3.9.1.drv-0/compiler-rt-3.9.1.src/lib/esan/esan_sideline_linux.cpp: In static member function ‘static int __esan::SidelineThread::runSideline(void*)’:
  /tmp/guix-build-clang-runtime-3.9.1.drv-0/compiler-rt-3.9.1.src/lib/esan/esan_sideline_linux.cpp:73:22: error: aggregate ‘__esan::SidelineThread::runSideline(void*)::sigaltstack SigAltStack’ has incomplete type and cannot be defined

Patch from <https://github.com/google/sanitizers/issues/822>.

index d04f5909d..bc272dfe4 100644
--- a/lib/esan/esan_sideline_linux.cpp
+++ b/lib/esan/esan_sideline_linux.cpp
@@ -70,7 +70,7 @@ int SidelineThread::runSideline(void *Arg) {
 
   // Set up a signal handler on an alternate stack for safety.
   InternalScopedBuffer<char> StackMap(SigAltStackSize);
-  struct sigaltstack SigAltStack;
+  stack_t SigAltStack;
   SigAltStack.ss_sp = StackMap.data();
   SigAltStack.ss_size = SigAltStackSize;
   SigAltStack.ss_flags = 0;
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<tr><td><span title='2018-09-04 17:25:11 +0200'>2018-09-04</span></td><td><a href='/guix/commit/m4?id=ca719424455465fca4b872c371daf2a46de88b33'>Switch to Guile-Gcrypt.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-06-01 15:35:15 +0200'>2018-06-01</span></td><td><a href='/guix/commit/m4?id=d59e75f3b5b82692bd250a1a3a9965397bb588c5'>build: Check for Guile-SQLite3.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
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<tr><td><span title='2018-01-06 14:45:01 +0100'>2018-01-06</span></td><td><a href='/guix/commit/m4?id=142182514b84ee233bc27e574df2ca2074291525'>build: Detect broken 'equal?' in Guile 2.2.1.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-06-30 00:16:50 +0200'>2017-06-30</span></td><td><a href='/guix/commit/m4?id=1d97fd8cb60f0b5f386f834940f859ff0b0bcc71'>build: Remove check for broken (srfi srfi-37).</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-02-20 12:58:07 +0200'>2017-02-20</span></td><td><a href='/guix/commit/m4?id=3b88f3767d9f3ad2cc64173525cd53d429bfe7e7'>gnu: Add bootstrap-binaries for 'aarch64-linux'.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2016-11-25 23:44:20 +0100'>2016-11-25</span></td><td><a href='/guix/commit/m4?id=21531add3205e400707c8fbfd841845f9a71863a'>offload: Use Guile-SSH instead of GNU lsh.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-08-10 15:40:22 -0400'>2016-08-10</span></td><td><a href='/guix/commit/m4?id=4ed40a3e6ca030573ded52233bd9e72dcdb85697'>build: Correctly determine the system type for GNU/Hurd systems.</a><span class='msg-avail'>...</span></td><td>Manolis Ragkousis</td></tr>
<tr><td><span title='2016-07-20 11:42:17 +0200'>2016-07-20</span></td><td><a href='/guix/commit/m4?id=7575655212ecfbcd1f04e429c8a7a41f8720d027'>Merge branch 'master' into core-updates</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-07-19 00:07:12 +0200'>2016-07-19</span></td><td><a href='/guix/commit/m4?id=721539026dda02e58addbb618f2102b31a2927f8'>Add (guix zlib).</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
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