the _builddir should never been used bu abuild due to the _ prefix.

the _ prefix is reserved for APKBUILD. This is to avoid use variable
names in APKBUILD that may clash with abuilds internal vars

consistent result regardless of current setting

To do so you need to set the patch_args variable to your desired
command line flags.

it's a regular expression, not shell pattern. empty match will
match everything (default is ^user\\.)

Do not add prepare() to new APKBUILDs in the future, as this
functionality is superseded by the addition of the default prepare
patcher in abuild.