Add -fcommon to autotools + meson (and fix some warnings)
While this does not fix the multiple definitions, it allows the code to compile "by default", so also outside of the CI.
Ref: #22 (closed), #23 (closed)
Additionally, fix various compiler warnings.
NOTE: for autotools, this change means that the autoconf-archive
package needs to be present because of the use of AX_APPEND_FLAG
.
Signed-off-by: Johannes Kauffmann johanneskauffmann@hotmail.com