www/firefox: fix build on aarch64
The interface has changed a bit on -current:
In file included from Unified_cpp_gfx_skia1.cpp:137:
/wrkdirs/usr/ports/www/firefox/work/firefox-71.0/gfx/skia/skia/src/core/SkCpu.cpp:81:13: error: use of undeclared identifier 'ID_AA64ISAR0_CRC32'
if (ID_AA64ISAR0_CRC32(id_aa64isar0) == ID_AA64ISAR0_CRC32_BASE) {
PR: 243653
Reviewed by: jbeich
Approved by: jbeich , manu (mentor, implicit)