www/firefox{,-esr} mail/thunderbird: pet CPUTYPE builds

some combinations of custom CPUTYPE and compiler require special
linker/compiler flags - try to chase this.

PR: 277021
PR: 281404
Submitted by: jkim@ (based on)

(cherry picked from commit c67ddb28c68d0f6bc1cd72d976ef7739a79e9089)