[build] cleanup low-hanging autoreconf warnings

Some uses of GNU make extensions were not necessary.  There are still some,
but they might exist as workarounds for older versions of autoconf that have
since been solved.

Lesson learned: implicit target rules have opposite order to pattern target
rules.
diff --git a/solaris/Makefile.am b/solaris/Makefile.am
index 674f4eb..ecaf9b9 100644
--- a/solaris/Makefile.am
+++ b/solaris/Makefile.am
@@ -10,16 +10,16 @@
 pkg_names = daemons dev doc libs smf
 pkg_quagga_daemons = zebra bgpd ospfd ospf6d ripd ripngd
 pkg_name_rev = @PACKAGE_VERSION@-@CONFDATE@-@target_os@-@target_cpu@
-pkg_depends := $(pkg_names:%=depend.%)
-pkg_packages := $(pkg_names:%=@PACKAGE_TARNAME@-%-$(pkg_name_rev).pkg)
-pkg_pkginfos := $(pkg_names:%=pkginfo.%.full)
-pkg_prototypes := $(pkg_names:%=prototype.%)
-pkg_manifests := quagga.xml
+pkg_depends = $(pkg_names:%=depend.%)
+pkg_packages = $(pkg_names:%=@PACKAGE_TARNAME@-%-$(pkg_name_rev).pkg)
+pkg_pkginfos = $(pkg_names:%=pkginfo.%.full)
+pkg_prototypes = $(pkg_names:%=prototype.%)
+pkg_manifests = quagga.xml
 
 # pkgmk variable substitutions wont grok ${variable} in prototype
 # file, so we cant let autoconf generate the file sadly
 # wish automake would just provide a template for this
-edit := $(SED) \
+edit = $(SED) \
 	-e 's,@prefix\@,$(prefix),g' \
 	-e 's,@exec_prefix,$(exec_prefix),g' \
 	-e 's,@bindir\@,$(bindir),g' \
@@ -47,7 +47,7 @@
  	-e 's,[@]target_os[@],$(target_os),g'
 
 # common options for pkgmk
-pkg_make_vars := exec_prefix=@exec_prefix@ prefix=@prefix@ \
+pkg_make_vars = exec_prefix=@exec_prefix@ prefix=@prefix@ \
 	builddir=@builddir@ srcdir=@srcdir@ \
 	top_builddir=@top_builddir@ top_srcdir=@top_srcdir@ \
 	abs_builddir=@abs_builddir@ abs_srcdir=@abs_srcdir@ \
@@ -110,9 +110,9 @@
 BUILT_SOURCES = $(pkg_pkginfos) pkginfo.tmpl $(pkg_prototypes) \
 	$(pkg_manifests) $(pkg_depends) quagga.init
 
-CLEANFILES := $(BUILT_SOURCES) $(pkg_packages)
+CLEANFILES = $(BUILT_SOURCES) $(pkg_packages)
 
-EXTRA_DIST := $(pkg_manifests:%=%.in) $(pkg_prototypes:%=%.in) \
+EXTRA_DIST = $(pkg_manifests:%=%.in) $(pkg_prototypes:%=%.in) \
 	$(pkg_names:%=pkginfo.%.tmpl.in) $(srcdir)/pkginfo.tmpl.in \
 	$(pkg_depends:%=%.in) quagga.init.in README.txt