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='2016-12-14 21:58:32 +0100'>2016-12-14</span></td><td><a href='/guix/commit/d3.v3.js?id=4d93f312f084c34a70cf7da3abe5f92a74d76861'>graph: Add d3js backend.</a><span class='msg-avail'>...<span class='msg-tooltip'>* d3.v3.js, graph.js: New files.
* Makefile.am (EXTRA_DIST): List them.
* guix/graph.scm (%d3js-backend): New variable.
(emit-d3js-prologue, emit-d3js-epilogue, emit-d3js-node,
emit-d3js-edge): New procedures.
(%graph-backends): Add %d3js-backend.
</span></span></td><td>Ricardo Wurmus</td></tr>