Don't force use of -fPIE for the dbus-daemon if apparently supported

Don't force use of -fPIE for the dbus-daemon if apparently supported

It's a minor security benefit, but not automatically beneficial (it
enables ASLR, but breaks prelinking, some buggy toolchains, and some gdb
versions). Distributions who know their infrastructure works well can
enable it just as easily via

    ./configure CFLAGS="-fPIE" LDFLAGS="-pie"

without extra support from us, and that's a generic solution applicable to
many packages.

Similarly, don't force libdbus and libdbus-internal to be PIC: libtool
knows better than we do whether that's necessary/beneficial on a
particular platform.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=16621
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=27215
Bug-NB: NB#171940
Reviewed-by: Colin Walters <walters@verbum.org>