Update SSC to latest version

[jerluc]

This includes various changes to support building libssc from it's latest release tag (2020.2.29_Release), which had some additional fallout associated:

• Split up into separate download, build, and install scripts in order to allow arbitrary code patching post-download but pre-build; this also makes it a little easier to debug
• Created two separate Docker builds: Alpine Linux and Ubuntu; this has helped me debug various build failures due to difference in environments (namely glibc vs. musl-libc)
• Created a patched nlopt/timer.c file to account for time.h/sys/time.h differences between glibc and musl-libc
• Updated build script to produce an optimized build output via CMake (in earlier versions of SSC, we had used simple Makefiles)

[ccma14]

This includes various changes to support building libssc from it's latest release tag (2020.2.29_Release), which had some additional fallout associated:

• Split up into separate download, build, and install scripts in order to allow arbitrary code patching post-download but pre-build; this also makes it a little easier to debug
• Created two separate Docker builds: Alpine Linux and Ubuntu; this has helped me debug various build failures due to difference in environments (namely glibc vs. musl-libc)
• Created a patched nlopt/timer.c file to account for time.h/sys/time.h differences between glibc and musl-libc
• Updated build script to produce an optimized build output via CMake (in earlier versions of SSC, we had used simple Makefiles)

@jerluc I pushed a change onto the branch that does not require a patched version of timer.c. In a nutshell, the nlopt code snapshot that is checked into ssc contains its own copies of sys/time.h and since a cmake build adds an explicit include directive pointing to the original source location (due to an out-of-tree build process), we pick up those during the build process rather than the system-provided ones.

IMHO these include files should not be checked into nlopt to begin with...