[Makefilea] Fix for GNU make < 4

Closes #9387

The shell assignment operator != was introduced in GNU make 4.0, or
specifically the commit in [1]. This fix removes such usages and
fallback to a more portable syntax. Tested with:

* GNU make 3.82 on CentOS 7.2
* bmake 20150910 on CentOS 7.2, source RPM from Fedora 24 [2]
* GNU make 4.2.1 on Arch Linux (Arch official package)
* bmake 20160926 on Arch Linux (Arch official package)
* GNU make 3.82 on Arch Linux (Compiled from source)
* Apple bsdmake-24 on macOS Sierra, binary package from Homebrew

Thanks @bdeyal for the feedback of the first tests

[1] http://git.savannah.gnu.org/cgit/make.git/commit/?id=b34438bee83ee906a23b881f257e684a0993b9b1
[2] http://koji.fedoraproject.org/koji/buildinfo?buildID=716769

ChangeLog

@@ -1,3 +1,9 @@
+version <unreleased>
+
+Core
+* Support for GNU make < 4 is fixed (#9387)
+
+
 version 2016.10.02
 
 Core

Makefile

@@ -12,7 +12,7 @@ SHAREDIR ?= $(PREFIX)/share
 PYTHON ?= /usr/bin/env python
 
 # set SYSCONFDIR to /etc if PREFIX=/usr or PREFIX=/usr/local
-SYSCONFDIR != if [ $(PREFIX) = /usr -o $(PREFIX) = /usr/local ]; then echo /etc; else echo $(PREFIX)/etc; fi
+SYSCONFDIR = $$(if [ $(PREFIX) = /usr -o $(PREFIX) = /usr/local ]; then echo /etc; else echo $(PREFIX)/etc; fi)
 
 install: youtube-dl youtube-dl.1 youtube-dl.bash-completion youtube-dl.zsh youtube-dl.fish
 	install -d $(DESTDIR)$(BINDIR)
@@ -90,7 +90,7 @@ fish-completion: youtube-dl.fish
 
 lazy-extractors: youtube_dl/extractor/lazy_extractors.py
 
-_EXTRACTOR_FILES != find youtube_dl/extractor -iname '*.py' -and -not -iname 'lazy_extractors.py'
+_EXTRACTOR_FILES = $$(find youtube_dl/extractor -iname '*.py' -and -not -iname 'lazy_extractors.py')
 youtube_dl/extractor/lazy_extractors.py: devscripts/make_lazy_extractors.py devscripts/lazy_load_template.py $(_EXTRACTOR_FILES)
 	$(PYTHON) devscripts/make_lazy_extractors.py $@