String literals are const in C++. Using this warnings moves us closer to
the stated goal of C++ compatibility, makes the code cleaner and lets
compilers optimize the code better.
Add m4/ax_append_compile_flags.m4 from Autoconf Archives for the
AX_APPEND_COMPILE_FLAGS macro and m4/ax_check_compile_flag.m4 as its
dependency.
Add Autoconf archive macros to check for -Wall and its dependencies.
Adjust m4/.gitignore to only ignore libtool macros.
Require Autoconf 2.65 for compatibility with Autoconf archive macros.
Keeping separate files is more maintainable than merging them into a
single aclocal.m4 file. It is easier for users to understand where those
files come from.
Automake knows how to distribute files in the m4 directory.
Pavel Roskin