_BSD_SOURCE has been depracted in glibc since 2.20 [1] and any compilation unit including a header from glibc will trigger a warning because _BSDSOURCE is defined in wvdial's CPPFLAGS.  Define _DEFAULT_SOURCE which is the replacement for _BSD_SOURCE and prevents the warning.

[1]: https://sourceware.org/legacy-ml/libc-alpha/2014-09/msg00088.html

Patch from Gentoo [1].

[1]:  https://gitweb.gentoo.org/repo/gentoo.git/tree/net-dialup/wvdial/files/wvdial-1.61-destdir.patch

Patch from Gentoo [1].

[1]: https://gitweb.gentoo.org/repo/gentoo.git/tree/net-dialup/wvdial/files/wvdial-1.61-parallel-make.patch

This is caused by --as-needed in LDFLAGS and incorret ordering of link options in the Makefile.  Fixed with a patch from Debian [1] that moves the libraries to linked with from LDFLAGS to the LIBS in Makefile.in.

[1]: https://sources.debian.org/data/main/w/wvdial/1.61-7/debian/patches/020_ftbfs_with_gcc_4.5.patch

FTR, commands used to change arch=() and then verify the changes:

$ sed -Ei "/^arch=/{s/ *?['\"]?i686['\"]? *?//;s/ *$//}" */*/PKGBUILD*

$ grep -r i686 * | grep arch= | grep -v repos

$ svn diff | grep -A 1 ^-[^-] | grep -v -- -- | cut -c2- |
  while IFS=$'\n' read -r l1; IFS=$'\n' read -r l2; do
    echo "$l1 -> $l2"
  done | sort -u