'asm/hwcap.h' file not found building chromium on Pi3

[Christoph Moench-Tegeder]

## bob prohaska (fbsd at www.zefox.net):

> The ports were updated to 537591, which seems to have updated
> www/chromium to chromium-83.0.4103.61, but the error persists.

asm/hwcap.h does not exist on FreeBSD. That somewhat modified
zlib code tries to include asm/hwcap.h as it believes it's building
on/for Linux on ARM (that #include is guarded by #ifdef ARMV8_OS_LINUX).
Even on Linux, asm/hwcap.h only exists on arm, riscv and some other
platforms, but notably not on anything x86-related.
As to "modified": the whole cpu_features.c is not part of the original
zlib distribution. So, I guess you're in for a deep dive...

Anyhow, ARMV8_OS_LINUX is passed in via BUILD.gn as part of some
optimization flags ("use_arm_neon_optimizations") - perhaps it's
possible to just skip that? But in the end, someone with ARM
knowledge should have a look at this; I'd guess that FreeBSD has some
other way of doing CPU feature detection for ARM. While there:
the whole cpu_features.c file is full of OS and CPU specific
code (well, that's the raison d'être for that file) and will need
a good going-over before it will work on FreeBSD/arm.

Regards,
Christoph

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