build: Remove spaces from variable-printing rules

This simplifies parsing when using these rules from scripts.

Makefile.am

@@ -4,7 +4,7 @@
 
 # Pattern rule to print variables, e.g. make print-top_srcdir
 print-%:
-	@echo '$*' = '$($*)'
+	@echo '$*'='$($*)'
 
 ACLOCAL_AMFLAGS = -I build-aux/m4
 SUBDIRS = src