BUG/MINOR: build: handle whitespaces in wc -l output

Certain implementations (for example ksh/OpenBSD) prefix the
'wc -l' output with whitespaces. This breaks the build since
689e4d733 ("BUILD: simplify the date and version retrieval in
the makefile").

Fix this by piping the wc output into tr -dc '0-9'.

Workaround is to build with IGNOREGIT=1.

HAProxy-1.4 is affected as well.
diff --git a/Makefile b/Makefile
index d47e676..f95ba03 100644
--- a/Makefile
+++ b/Makefile
@@ -354,7 +354,7 @@
 VERSION := $(shell [ -d .git/. ] && ref=`(git describe --tags --match 'v*' --abbrev=0) 2>/dev/null` && ref=$${ref%-g*} && echo "$${ref\#v}")
 ifneq ($(VERSION),)
 # OK git is there and works.
-SUBVERS := $(shell comms=`git log --format=oneline --no-merges v$(VERSION).. 2>/dev/null | wc -l`; [ $$comms -gt 0 ] && echo "-$$comms")
+SUBVERS := $(shell comms=`git log --format=oneline --no-merges v$(VERSION).. 2>/dev/null | wc -l | tr -dc '0-9'`; [ $$comms -gt 0 ] && echo "-$$comms")
 VERDATE := $(shell git log -1 --pretty=format:%ci | cut -f1 -d' ' | tr '-' '/')
 endif
 endif