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='2020-03-16 14:05:52 +0100'>2020-03-16</span></td><td><a href='/guix/commit/gnu/tests/rsync.scm?id=4df02ab675b262bc2d43f83ad33785eb434ea6cb'>tests: rsync: Set PATH.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is a followup to 8b9cad01e9619f53dc5a65892ca6a09ca5de3447, which
would leave PATH unset.

* gnu/tests/rsync.scm (run-rsync-test)[test]("service running"): Add
call to 'setenv' for PATH.
</span></span></td><td>Ludovic Courtès</td></tr>