configure: allows to silent compilation

* HACKING, configure.ac: here.

HACKING

@@ -109,6 +109,16 @@ another "magic touch":
 
   touch doc/org-stamp
 
+Silent Building with automake
+-----------------------------
+
+The classical makefiles generated by automake are very verbose during
+build beacause they prints the full command line of every stage. This
+verbosity is very usefull to help (remotely) users to compile
+Spot. Nonetheless, for developpers, these compilations lines may be
+annoying. To reduce this verbosity, just run:
+
+  make V=0
 
 Debugging Libtool executables
 -----------------------------

configure.ac

@@ -44,6 +44,9 @@ AC_PROG_CXX
 AM_PROG_LEX
 adl_CHECK_BISON
 
+# Decrease verbosity when passing argument V=0
+AM_SILENT_RULES([no])
+
 # Option to activate C/C++14
 AC_ARG_ENABLE([c++14],
               [AC_HELP_STRING([--enable-c++14],