This fixes

../../../../gcc-7.4.0/libstdc++-v3/libsupc++/new_opa.cc: In function ‘void* __gnu_cxx::aligned_alloc(std::size_t, std::size_t)’:
../../../../gcc-7.4.0/libstdc++-v3/libsupc++/new_opa.cc:78:10: error: ‘memalign’ was not declared in this scope
   return memalign (al, sz);
          ^~~~~~~~
../../../../gcc-7.4.0/libstdc++-v3/libsupc++/new_opa.cc:78:10: note: suggested alternative: ‘max_align_t’
   return memalign (al, sz);
          ^~~~~~~~
          max_align_t

diff --git a/libstdc++-v3/libsupc++/new_opa.cc b/libstdc++-v3/libsupc++/new_opa.cc
index 94e79cadb0e..084900e0daf 100644
--- a/libstdc++-v3/libsupc++/new_opa.cc
+++ b/libstdc++-v3/libsupc++/new_opa.cc
@@ -39,6 +39,8 @@ extern "C" void *memalign(std::size_t boundary, std::size_t size);
 # endif
 #endif
 
+#define memalign _aligned_malloc
+
 using std::new_handler;
 using std::bad_alloc;
 
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<div class='path'>path: <a href='/guix/log/?id=6858ade2e56b9c4573bc8ba191cd63af997abd5d&amp;ofs=100'>root</a>/<a href='/guix/log/gnu?id=6858ade2e56b9c4573bc8ba191cd63af997abd5d&amp;ofs=100'>gnu</a>/<a href='/guix/log/gnu/system.scm?id=6858ade2e56b9c4573bc8ba191cd63af997abd5d&amp;ofs=100'>system.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/system.scm?id=6858ade2e56b9c4573bc8ba191cd63af997abd5d&amp;ofs=100&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2016-10-30 22:59:46 +0100'>2016-10-30</span></td><td><a href='/guix/commit/gnu/system.scm?id=1ef8b72a7f87afe7cffe52393d99e1b14e4770e1'>system: Record store file system info in each generation.</a><span class='msg-avail'>...</span></td><td>Chris Marusich</td></tr>
<tr><td><span title='2016-09-30 12:05:27 +0200'>2016-09-30</span></td><td><a href='/guix/commit/gnu/system.scm?id=79355ae3e84359716f5135cc7083e72246bc8bf9'>Merge branch 'master' into core-updates</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-09-24 17:48:13 +0900'>2016-09-24</span></td><td><a href='/guix/commit/gnu/system.scm?id=0f65f54ebd76324653fd5506a7dab42ee44d9255'>system: grub.cfg uses correct file names when store is not in root partition.</a><span class='msg-avail'>...</span></td><td>Carlos Sánchez de La Lama</td></tr>
<tr><td><span title='2016-09-24 17:48:12 +0900'>2016-09-24</span></td><td><a href='/guix/commit/gnu/system.scm?id=d7b342d81556ddee9e369f78255bc76367a004ae'>system: 'read-boot-parameters' reads the 'initrd' parameter.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-09-10 13:10:06 +0200'>2016-09-10</span></td><td><a href='/guix/commit/gnu/system.scm?id=9e41130b14ad32c4e1fa756f95d806703056cb60'>system: Use 'file-append' to denote file names.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-09-09 23:54:44 +0200'>2016-09-09</span></td><td><a href='/guix/commit/gnu/system.scm?id=ab20d74a4638dc6295aa9b9af276d2a98f238f9d'>system: Build the initrd file name with 'file-append'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-09-09 23:54:43 +0200'>2016-09-09</span></td><td><a href='/guix/commit/gnu/system.scm?id=44d5f54e31039d78f156bd9562dca293124eaa76'>system: grub: Allow arbitrary kernel file names in 'menu-entry'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-08-29 23:46:33 +0300'>2016-08-29</span></td><td><a href='/guix/commit/gnu/system.scm?id=b3d2be945d2dfe08e3b73102dd0fd3f4a0a93b60'>Merge remote-tracking branch 'origin/master' into core-updates</a></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2016-08-22 00:20:48 +0200'>2016-08-22</span></td><td><a href='/guix/commit/gnu/system.scm?id=aa1145df8d43187f3e92aa505298cdeca4fb1191'>services: Make a single extensible 'file-systems' service.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-08-10 15:41:21 -0400'>2016-08-10</span></td><td><a href='/guix/commit/gnu/system.scm?id=9f58fe3d1c32e3f0ced065e286532a10cad1b5e3'>gnu: glibc/linux: Adjust variable name to upstream change.</a><span class='msg-avail'>...</span></td><td>Leo Famulari</td></tr>
<tr><td><span title='2016-08-02 18:07:19 +0200'>2016-08-02</span></td><td><a href='/guix/commit/gnu/system.scm?id=ab3a64507a792e4da0527b423fbc28f8768e736a'>system: Define 'GUIX_LOCPATH' to work around 'glibc' package defect.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>