Fix build with FreeType 2.10.3 and newer.

Taken from upstream:
https://git.ghostscript.com/?p=ghostpdl.git;a=commitdiff;h=41ef9a0bc36b9db7115fbe9623f989bfb47bbade

diff --git a/base/fapi_ft.c b/base/fapi_ft.c
--- a/base/fapi_ft.c
+++ b/base/fapi_ft.c
@@ -125,7 +125,7 @@ static void
 delete_inc_int_info(gs_fapi_server * a_server,
                     FT_IncrementalRec * a_inc_int_info);
 
-FT_CALLBACK_DEF(void *)
+static void *
 FF_alloc(FT_Memory memory, long size)
 {
     gs_memory_t *mem = (gs_memory_t *) memory->user;
@@ -133,7 +133,7 @@ FF_alloc(FT_Memory memory, long size)
     return (gs_malloc(mem, size, 1, "FF_alloc"));
 }
 
-FT_CALLBACK_DEF(void *)
+static void *
     FF_realloc(FT_Memory memory, long cur_size, long new_size, void *block)
 {
     gs_memory_t *mem = (gs_memory_t *) memory->user;
@@ -153,7 +153,7 @@ FT_CALLBACK_DEF(void *)
     return (tmp);
 }
 
-FT_CALLBACK_DEF(void)
+static void
     FF_free(FT_Memory memory, void *block)
 {
     gs_memory_t *mem = (gs_memory_t *) memory->user;
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<div class='path'>path: <a href='/guix/commit/?id=354c493fb8212e15f6bdb308375f7331eee0374a'>root</a>/<a href='/guix/commit/gnu?id=354c493fb8212e15f6bdb308375f7331eee0374a'>gnu</a>/<a href='/guix/commit/gnu/packages?id=354c493fb8212e15f6bdb308375f7331eee0374a'>packages</a>/<a href='/guix/commit/gnu/packages/bioinformatics.scm?id=354c493fb8212e15f6bdb308375f7331eee0374a'>bioinformatics.scm</a></div><div class='content'><div class='cgit-panel'><b>diff options</b><form method='get'><input type='hidden' name='id' value='354c493fb8212e15f6bdb308375f7331eee0374a'/><table><tr><td colspan='2'/></tr><tr><td class='label'>context:</td><td class='ctrl'><select name='context' onchange='this.form.submit();'><option value='1'>1</option><option value='2'>2</option><option value='3' selected='selected'>3</option><option value='4'>4</option><option value='5'>5</option><option value='6'>6</option><option value='7'>7</option><option value='8'>8</option><option value='9'>9</option><option value='10'>10</option><option value='15'>15</option><option value='20'>20</option><option value='25'>25</option><option value='30'>30</option><option value='35'>35</option><option value='40'>40</option></select></td></tr><tr><td class='label'>space:</td><td class='ctrl'><select name='ignorews' onchange='this.form.submit();'><option value='0' selected='selected'>include</option><option value='1'>ignore</option></select></td></tr><tr><td class='label'>mode:</td><td class='ctrl'><select name='dt' onchange='this.form.submit();'><option value='0' selected='selected'>unified</option><option value='1'>ssdiff</option><option value='2'>stat only</option></select></td></tr><tr><td/><td class='ctrl'><noscript><input type='submit' value='reload'/></noscript></td></tr></table></form></div><table summary='commit info' class='commit-info'>
<tr><th>author</th><td>Leo Famulari &lt;leo@famulari.name&gt;</td><td class='right'>2018-02-10 13:46:22 -0500</td></tr>
<tr><th>committer</th><td>Leo Famulari &lt;leo@famulari.name&gt;</td><td class='right'>2018-02-10 13:47:58 -0500</td></tr>
<tr><th>commit</th><td colspan='2' class='oid'><a href='/guix/commit/gnu/packages/bioinformatics.scm?id=354c493fb8212e15f6bdb308375f7331eee0374a'>354c493fb8212e15f6bdb308375f7331eee0374a</a> (<a href='/guix/patch/gnu/packages/bioinformatics.scm?id=354c493fb8212e15f6bdb308375f7331eee0374a'>patch</a>)</td></tr>
<tr><th>tree</th><td colspan='2' class='oid'><a href='/guix/tree/?id=354c493fb8212e15f6bdb308375f7331eee0374a'>64300eeda7ee8ee90b605a5b79c80d27f615c66b</a> /<a href='/guix/tree/gnu/packages/bioinformatics.scm?id=354c493fb8212e15f6bdb308375f7331eee0374a'>gnu/packages/bioinformatics.scm</a></td></tr>
<tr><th>parent</th><td colspan='2' class='oid'><a href='/guix/commit/gnu/packages/bioinformatics.scm?id=73a1f10a80397597436d08e1992412148dbceea8'>73a1f10a80397597436d08e1992412148dbceea8</a> (<a href='/guix/diff/gnu/packages/bioinformatics.scm?id=354c493fb8212e15f6bdb308375f7331eee0374a&amp;id2=73a1f10a80397597436d08e1992412148dbceea8'>diff</a>)</td></tr><tr><th>download</th><td colspan='2' class='oid'><a href='/guix/snapshot/guix-354c493fb8212e15f6bdb308375f7331eee0374a.tar.gz'>guix-354c493fb8212e15f6bdb308375f7331eee0374a.tar.gz</a><br/><a href='/guix/snapshot/guix-354c493fb8212e15f6bdb308375f7331eee0374a.zip'>guix-354c493fb8212e15f6bdb308375f7331eee0374a.zip</a><br/></td></tr></table>
<div class='commit-subject'>gnu: exim: Update to 4.90.1 [fixes CVE-2018-6789].</div><div class='commit-msg'>* gnu/packages/mail.scm (exim): Update to 4.90.1.
[source]: Use HTTPS URLs.
</div><div class='diffstat-header'><a href='/guix/diff/?id=354c493fb8212e15f6bdb308375f7331eee0374a'>Diffstat</a> (limited to 'gnu/packages/bioinformatics.scm')</div><table summary='diffstat' class='diffstat'></table><div class='diffstat-summary'>0 files changed, 0 insertions, 0 deletions</div><table summary='diff' class='diff'><tr><td></td></tr></table></div> <!-- class=content -->
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