build: do not quote `like this', as per GCS recommendation

build: do not quote `like this', as per GCS recommendation

This patch converts the files implementing the automake's own build
system to the use of new quoting format 'like this' or "like this"
rather than `like this'.

* bootstrap, configure.ac, syntax-checks.mk, Makefile.am,
lib/Makefile.am, m4/Makefile.am, syntax-checks.mk: Update quoting
format throughout, in comments and diagnostic.  Some minor related
rewordings and reformatting since we are at it.