Add support to parse build params from _buildparams file

[bmwiedemann]

To allow for custom build tweaks such as -j1 and
--vm-custom-opt=-cpu qemu64 written as separate lines in the _buildparams file.

This includes regexp whitelist validation to minimize risk to OBS operations.

The pattern for jobs deliberately does not have a * or + to not allow DoS or integer overflows.

The pattern for CPU allows to enable or disable individual CPUID flags. IMHO this should be safe.

[adrianschroeter]

After some discussion, a possible way to implement this could be via buildflags. eg.

#!BuildFlags: cputype:$KNOWN_GOOD_CPU_TYPE

the known good cpu type may cause issues when eg. an AMD cpu gets enforced on a Intel hardware? But at least cpu types like "qemu64" on x86_64 could be supported here.

Alternative/Additionally we may support

#!BuildFlags: cpuflag:$FLAG

FLAG can be for example "-avx" to disable avx support.

This way we can have architecture specific definitions, because these can be sourounded via %ifarch statements.

[mlschroe]

To be honest, I don't like this at all. Which packages would need this at all? If this is a very small list, can't that be fixed in the packages in a different and more sane way?

[bmwiedemann]

There is a small list:

• colord (AVX2)
• calibre (SSE-4.1)
• emacs (very sensitive to CPU changes)
• (not counting the dozen packages that used -march=native that we already patched)

These are still left after quite some time.

I agree that this patch is somewhat dirty and we probably need something nicer - that is why I had opened https://jira.suse.com/browse/OBS-362