Stripped and musl build options

[fntlnz]

This patch adds two new build options to the project

CMake options	Meaning
-DMINIMAL_BUILD=On	Build without docker, cri, mesos, marathon and kubernetes support
-DMUSL_OPTIMIZED_BUILD=On	Build targeting musl libc instead of glibc. musl-libc must be provided by the target system. To produce a 100% statically linked sysdig binary, this will need to be used along with -DUSE_BUNDLED_DEPS=On

These options can be used together to accomplish a minimal build that uses musl libc.

Todo:

• Implement the new options
• Find a solution to replace getaddrinfo_a
  • right now we did it by doing a dumb wrapper (that will need to be changed before we merge this PR)
  • done using c-ares gethostbyname

How to compile a static binary using musl?

The easiest way is to:

docker run -v /source/sysdig:/sysdig -it alpine:3.12 sh
# in the container
apk update && apk add g++ gcc cmake cmake make  ncurses-dev git bash perl linux-headers autoconf  automake m4 libtool elfutils-dev libelf-static patch
cd /sysdig
mkdir build
cd build
cmake -DMUSL_OPTIMIZED_BUILD=True -DUSE_BUNDLED_DEPS=True ..
make -j16 sysdig

Goals

The main goal is to produce a 100% static sysdig binary that has no dependencies on the host libc and libraries.

Fixes #903

[leogr]

👏

[rofl0r]

that's hell of a PR just to circumvent lack of getaddrinfo_a in POSIX conformant libcs.
what i'd have prefered instead would've been

• a configure-style check whether getaddrinfo_a is available
• if not, use plain getaddrinfo

instead we get a "musl profile", an embedded 3rd party library and lots of cmake options...

[richfelker]

The changes made for build problems with musl did not fix the problem but encoded a dependency on implementation details which are not public interfaces. Comments inline. Hope this worked right - it's my first time using the GitHub review system.

[richfelker]

These macros are not public interfaces. If they're fixing a build error for you, the underlying problem is that the file is failing to include <time.h>. All headers in bits are private implementation details and are only valid for inclusion from the other libc headers, not directly.

[fntlnz]

Thanks for taking the time to look at this @richfelker - I'll try to fix this. To be honest, I found those by looking at the musl source code directly, I wasn't aware of this detail so thanks!

[richfelker]

This should be <time.h> and it should probably be included at the point where the types are needed rather than here.

[fntlnz]

@rofl0r PRs are welcome!

[leodido]

@richfelker would you please take a look at #1684 if you can? :)

[richfelker]

LGTM