Minor improvements and extensions to various tests.

Minor improvements and extensions to various tests.

* tests/defun.test: Also run autoconf and grep the generated
configure to make sure that aclocal truly picks up all the
required macros.
* tests/compile_f_c_cxx.test: Prefer trailing `:' over trailing
`Exit 0'.  Do not create useless dummy source files.  Do not set
useless `$(foo_LDADD)' variable in `Makefile.am'.  Do not call
useless macro `AC_F77_LIBRARY_LDFLAGS' in `configure.in'.
* tests/compile_f90_c_cxx.test: Likewise.
* tests/suffix10.test: Slighty stricter grepping of make output.
* tests/compile.test: Add trailing `:' command.
* tests/defun2.test: Likewise.
* tests/vars3.test: Likewise.
* tests/vartar.test: Likewise.
* tests/vars.test: Likewise.  Also, extend test by checking
that the definition of `MY_FLAGS*' variables is preserved in
the generated `Makefile.in'.
* tests/stamph2.test: Prefer trailing `:' over trailing `Exit 0'.
Use proper m4 quoting in `configure.in'.