The libarchive header is used in alpm.h, and several binaries include
this header. This is noticeably a problem when using e.g. the musl-gcc
compiler which does not include /usr/include by default, and thus the
build system reports:
...../lib/libalpm/alpm.h:35:10: fatal error: archive.h: No such file or directory
More commonly, this will result in compiling against potentially the
wrong headers, if the libarchive installation picked up by pkg-config is
different from the one with headers in /usr/include, and /usr/include is
in the -isystem path.
Signed-off-by: Eli Schwartz