[CLEANUP] make makefile more old sh-friendly

Older SH on Solaris does not know about $(cmd) but only know `cmd`.
diff --git a/Makefile b/Makefile
index d3d5c97..a26d476 100644
--- a/Makefile
+++ b/Makefile
@@ -108,13 +108,13 @@
 # Now let's determine the version, sub-version and release date.
 # If we're in the GIT tree, we can use the last commit's version and date.
 ifeq ($(IGNOREGIT),)
-VERSION := $(shell [ -d .git/. ] && ref=$$(git-describe --tags 2>/dev/null) && ref=$${ref%-g*} && echo "$${ref\#v}" )
+VERSION := $(shell [ -d .git/. ] && ref=`git-describe --tags 2>/dev/null` && ref=$${ref%-g*} && echo "$${ref\#v}" )
 endif
 
 ifneq ($(VERSION),)
 # OK git is there and works.
-SUBVERS := $(shell comms=$$(git-log --no-merges v$(VERSION).. 2>/dev/null |grep -c ^commit ); [ $$comms -gt 0 ] && echo "-$$comms" )
-VERDATE := $(shell date +%Y/%m/%d -d "$$(git-log HEAD^.. 2>/dev/null | grep -m 1 ^Date: | cut -f2- -d: | cut -f1 -d+)" )
+SUBVERS := $(shell comms=`git-log --no-merges v$(VERSION).. 2>/dev/null |grep -c ^commit `; [ $$comms -gt 0 ] && echo "-$$comms" )
+VERDATE := $(shell date +%Y/%m/%d -d "`git-log HEAD^.. 2>/dev/null | grep -m 1 ^Date: | cut -f2- -d: | cut -f1 -d+`" )
 else
 # Otherwise, use the hard-coded version of last tag, number of changes
 # since last tag, and release date.