qemu -version output is incorrect with configure --with-pkgversion

Since qemu v2.7.0, up to the current master
(1883ff34b540daacae948f493b0ba525edf5f642)
the pkgversion feature appears to have a bug:

$ ./configure --target-list=x86_64-softmmu --with-pkgversion=foo

Results in this output:

$ x86_64-softmmu/qemu-system-x86_64 -version
QEMU emulator version 2.8.90(foo)
Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers

This appears to have been introduced in:

67a1de0d19 Makefile: Derive "PKGVERSION" from "git describe" by default

The previous commit (077de81a4c) produces this output:

$ x86_64-softmmu/qemu-system-x86_64 -version
QEMU emulator version 2.6.50 (foo), Copyright (c) 2003-2008 Fabrice Bellard