Snippets for aom 3.15.0 from Alpine armhf

Sourced from https://build.alpinelinux.org/buildlogs/build-edge-armhf/main/aom/aom-3.15.0-r0.log.

• /home/buildozer/aports/main/aom/src/libaom-3.15.0/aom_ports/aarch32_cpudetect.c:68:17: warning: unused variable 'hwcap' [-Wunused-variable]
     68 |   unsigned long hwcap = getauxval(AT_HWCAP);
        |                 ^~~~~