Fix configure.ac quoting of AC_CHECK_LIB's 2nd arg

Fix configure.ac quoting of AC_CHECK_LIB's 2nd arg

Running an autoconf-head-generated configure, would fail like this:
  /emacs/configure: line 18002: syntax error near unexpected token `;;'
  /emacs/configure: line 18002: `  ;;'
That is due to under-quoting of AC_CHECK_LIB's second argument, which led to
the comma in an embedded string being interpreted as paramater-delimiting.
* configure.ac: Quote the second arg of each AC_CHECK_LIB invocation.
(Bug#56272)

Copyright-paperwork-exempt: yes