[fork] document and/or fix unintuitive behavior

Some totally hypothetical scenario:

builder on aarch64 ~/packages/system/ruby $ ls -l /packages/system/aarch64/ruby-*
-rw-r--r-- 1 builder abuild     6978 Jan  9 16:38 /packages/system/aarch64/ruby-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild     6273 Jan  9 18:39 /packages/system/aarch64/ruby-3.4.1-r0.apk
-rw-r--r-- 1 builder abuild    58139 Jan  9 16:38 /packages/system/aarch64/ruby-bigdecimal-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    11000 Jan  9 18:39 /packages/system/aarch64/ruby-bigdecimal-3.4.1-r0.apk
-rw-r--r-- 1 builder abuild 10707628 Jan  9 16:38 /packages/system/aarch64/ruby-dbg-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild 11562991 Jan  9 18:39 /packages/system/aarch64/ruby-dbg-3.4.1-r0.apk
-rw-r--r-- 1 builder abuild   645527 Jan  9 16:38 /packages/system/aarch64/ruby-dev-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild  1207332 Jan  9 18:39 /packages/system/aarch64/ruby-dev-3.4.1-r0.apk
-rw-r--r-- 1 builder abuild  4149700 Jan  9 16:38 /packages/system/aarch64/ruby-doc-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild  4107394 Jan  9 18:39 /packages/system/aarch64/ruby-doc-3.4.1-r0.apk
-rw-r--r-- 1 builder abuild    37001 Jan  9 16:38 /packages/system/aarch64/ruby-fiddle-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    41214 Jan  9 18:39 /packages/system/aarch64/ruby-fiddle-3.4.1-r0.apk
-rw-r--r-- 1 builder abuild     1572 Jan  9 16:38 /packages/system/aarch64/ruby-full-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild     1572 Jan  9 18:39 /packages/system/aarch64/ruby-full-3.4.1-r0.apk
-rw-r--r-- 1 builder abuild    13361 Jan  9 16:38 /packages/system/aarch64/ruby-io-console-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    13918 Jan  9 18:39 /packages/system/aarch64/ruby-io-console-3.4.1-r0.apk
-rw-r--r-- 1 builder abuild    84512 Jan  9 16:38 /packages/system/aarch64/ruby-irb-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    87349 Jan  9 18:39 /packages/system/aarch64/ruby-irb-3.4.1-r0.apk
-rw-r--r-- 1 builder abuild    44682 Jan  9 16:38 /packages/system/aarch64/ruby-json-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    49323 Jan  9 18:39 /packages/system/aarch64/ruby-json-3.4.1-r0.apk
-rw-r--r-- 1 builder abuild  7401011 Jan  9 16:38 /packages/system/aarch64/ruby-libs-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild  7877167 Jan  9 18:39 /packages/system/aarch64/ruby-libs-3.4.1-r0.apk
-rw-r--r-- 1 builder abuild    93119 Jan  9 16:38 /packages/system/aarch64/ruby-minitest-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    98542 Jan  9 18:39 /packages/system/aarch64/ruby-minitest-3.4.1-r0.apk
-rw-r--r-- 1 builder abuild    13726 Jan  9 16:38 /packages/system/aarch64/ruby-power_assert-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    13776 Jan  9 18:39 /packages/system/aarch64/ruby-power_assert-3.4.1-r0.apk
-rw-r--r-- 1 builder abuild    90115 Jan  9 16:38 /packages/system/aarch64/ruby-rake-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    90212 Jan  9 18:39 /packages/system/aarch64/ruby-rake-3.4.1-r0.apk
-rw-r--r-- 1 builder abuild   628848 Jan  9 16:38 /packages/system/aarch64/ruby-rdoc-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild   637704 Jan  9 18:39 /packages/system/aarch64/ruby-rdoc-3.4.1-r0.apk
-rw-r--r-- 1 builder abuild   101135 Jan  9 16:38 /packages/system/aarch64/ruby-test-unit-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild   104832 Jan  9 18:39 /packages/system/aarch64/ruby-test-unit-3.4.1-r0.apk

builder on aarch64 ~/packages/system/ruby $ grep ^pkgver= APKBUILD 
pkgver=3.3.5
builder on aarch64 ~/packages/system/ruby $ abuild cleanoldpkg
>>> ruby: Cleaning all packages except 3.3.5-r0...
>>> ruby: Updating the system/aarch64 repository index...
>>> ruby: Signing the index...
builder on aarch64 ~/packages/system/ruby $ ls -l /packages/system/aarch64/ruby-*
-rw-r--r-- 1 builder abuild     6978 Jan  9 16:38 /packages/system/aarch64/ruby-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    58139 Jan  9 16:38 /packages/system/aarch64/ruby-bigdecimal-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild 10707628 Jan  9 16:38 /packages/system/aarch64/ruby-dbg-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild   645527 Jan  9 16:38 /packages/system/aarch64/ruby-dev-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild  4149700 Jan  9 16:38 /packages/system/aarch64/ruby-doc-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    37001 Jan  9 16:38 /packages/system/aarch64/ruby-fiddle-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild     1572 Jan  9 16:38 /packages/system/aarch64/ruby-full-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    13361 Jan  9 16:38 /packages/system/aarch64/ruby-io-console-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    84512 Jan  9 16:38 /packages/system/aarch64/ruby-irb-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    44682 Jan  9 16:38 /packages/system/aarch64/ruby-json-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild  7401011 Jan  9 16:38 /packages/system/aarch64/ruby-libs-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    93119 Jan  9 16:38 /packages/system/aarch64/ruby-minitest-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    13726 Jan  9 16:38 /packages/system/aarch64/ruby-power_assert-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild    90115 Jan  9 16:38 /packages/system/aarch64/ruby-rake-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild   628848 Jan  9 16:38 /packages/system/aarch64/ruby-rdoc-3.3.5-r0.apk
-rw-r--r-- 1 builder abuild   101135 Jan  9 16:38 /packages/system/aarch64/ruby-test-unit-3.3.5-r0.apk

builder on aarch64 ~/packages/system/ruby $ git checkout current
...
builder on aarch64 ~/packages/system/ruby $ grep ^pkgver= APKBUILD 
pkgver=3.4.1
builder on aarch64 ~/packages/system/ruby $ abuild cleanoldpkg
>>> ruby: Cleaning all packages except 3.4.1-r0...
>>> ruby: Updating the system/aarch64 repository index...
>>> ruby: Signing the index...
builder on aarch64 ~/packages/system/ruby $ ls -l /packages/system/aarch64/ruby-*
ls: cannot access '/packages/system/aarch64/ruby-*': No such file or directory

And that's how you end up with no Ruby at all! (Note: cleanpkg has a similar but possibly less disastrous effect).

Another case: abuild -rf

• If there is no change in pkgver or pkgrel, the -f may be required (otherwise "package is up to date")
• If the APKBUILD has arch="!ppc", then it might still try to build on ppc, and I don't want that.

Therefore:

• -f should NOT override arch= (and/or another flag like -F should be created to force it)