Fix build with GNU Make 4.3:

https://github.com/Aegisub/Aegisub/issues/171

Patch taken from upstream:

https://github.com/Aegisub/Aegisub/commit/6bd3f4c26b8fc1f76a8b797fcee11e7611d59a39

diff --git a/Makefile.target b/Makefile.target
--- a/Makefile.target
+++ b/Makefile.target
@@ -112,7 +112,7 @@ POST_FLAGS = $($@_FLAGS) -c -o $@ $<
 # Libraries contain all object files they depend on (but they may depend on other files)
 # Not using libtool on OS X because it has an unsilenceable warning about a
 # compatibility issue with BSD 4.3 (wtf)
-lib%.a: $$($$*_OBJ)
+lib%.a: $$($$(*F)_OBJ)
 	@$(BIN_MKDIR_P) $(dir $@)
 	$(BIN_AR) cru $@ $(filter %.o,$^)
 	$(BIN_RANLIB) $@
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<tr><td><span title='2017-12-31 11:18:30 +0100'>2017-12-31</span></td><td><a href='/guix/commit/nix/scripts/list-runtime-roots.in?id=091191c3dcbfb9f01070d26bf15cb2c4dd07b1b5'>list-runtime-root: Fix off-by-one in 'strip-drop' call.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/29862&gt;.
Reported by Danny Milosavljevic &lt;dannym@scratchpost.org&gt;.

* nix/scripts/list-runtime-roots.in (canonicalize-store-item): Define
'store' with a trailing "/".  Have the 'string-prefix?' call match the
'string-drop' call.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-11-26 15:58:33 +0100'>2017-11-26</span></td><td><a href='/guix/commit/nix/scripts/list-runtime-roots.in?id=9b0713012905f3997d6fad201dba7c3d93b38b13'>list-runtime-roots: Ignore ESRCH while reading from /proc.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/29368&gt;.
Reported by Martin Castillo &lt;castilma@uni-bremen.de&gt;.

* nix/scripts/list-runtime-roots.in (referenced-files): Ignore ESRCH.
</span></span></td><td>Ludovic Courtès</td></tr>