systemd: Explicitly set build type to Meson

It looks like, changes in bee build type ordering causes the error
below.

    [BEE] GNU autotools detection failed.
    [BEE] /dev/shm/bee-root/systemd/systemd-239-0/source/configure: does not seem to be generated
     by GNU autotools.
    [BEE] use BEE_BUILDTYPE=autotools to force it anyway
    [BEE] using magic buildtype 'make' from '/usr/libexec/bee/beesh.d/make.sh' ..
    [BEE]  -> B=S linking build dir /dev/shm/bee-root/systemd/systemd-239-0/build to source dir
    [BEE] changing to build directory: /dev/shm/bee-root/systemd/systemd-239-0/source
    [BEE] => entering mee_configure() ..
    /usr/bin/beesh: line 504: [: too many arguments
    [BEE] action 'bee_configure' is not defined: skipping..
    [BEE] <= leaving mee_configure() ..
    [BEE] => entering bee_build() ..
    [BEE] make -j100 PREFIX=/usr EPREFIX=/usr BINDIR=/usr/bin SBINDIR=/usr/sbin LIBEXECDIR=/usr/libexec SYSCONFDIR=/etc SHAREDSTATEDIR=/var LOCALSTATEDIR=/var LIBDIR=/usr/lib INCLUDEDIR=/usr/include DATAROOTDIR=/usr/share DATADIR=/usr/share INFODIR=/usr/share/info LOCALEDIR=/usr/share/locale MANDIR=/usr/share/man DOCDIR=/usr/share/doc/systemd
    ninja -C build
    ninja: Entering directory `build'
    ninja: fatal: chdir to 'build' - No such file or directory
    make: *** [Makefile:2: all] Error 1
    Command exited with non-zero status 2

Therefore, set the build type explicitly.

systemd.be0

@@ -17,6 +17,8 @@ SRCURL[0]="https://github.com/systemd/systemd/archive/v${PKGVERSION}.tar.gz"
 
 # PATCHURL+=()
 
+BEE_BUILDTYPE=meson
+
 ###############################################################################
 ## Add filename patterns to the EXCLUDE array of files that should not
 ## be added to you package but may be present in the image directory.