pmb.config: add the full hexdump to the list of installed build packages (MR 2454)

This works around https://gitlab.postmarketos.org/postmarketOS/
pmaports/-/issues/3268, by always installing hexdump when building
packages. The full hexdump is small (like 80KB), and even though this
isn't required in most situations it seems like the best of a group
of bad workarounds, until upstream/busybox fix the bug in the pmaports
issue.

pmb/config/__init__.py

@@ -211,7 +211,11 @@ chroot_outdated = 3600 * 24 * 2
 # for the first time
 # IMPORTANT: the order here matters, it is the order these packages will
 # be built in (if needed). abuild must be first!
-build_packages = ["abuild", "apk-tools", "build-base", "ccache", "git"]
+#
+# NOTE: full hexdump is installed to workaround a bug in busybox,
+# see https://gitlab.postmarketos.org/postmarketOS/pmaports/-/issues/3268. This can be
+# reverted when the bug is properly fixed.
+build_packages = ["abuild", "apk-tools", "build-base", "ccache", "git", "hexdump"]
 
 #
 # PARSE