ppc64le support: "preset" modification.

[asowani]

Ref.: #6
Build preset "buildbot_incremental_linux" has been tested in local VM setup and it executes build process correctly.

[shahmishal]

I don't see buildbot_incremental_linux,tools=RA,stdlib=RD in utils/build-presets.ini

If you are looking for Linux presets, this is what we currently have on master branch. However, you can always add new preset for ppc64le.

utils/build-presets.ini:[preset: buildbot_linux]
utils/build-presets.ini:[preset: buildbot_linux,no_test]
utils/build-presets.ini:[preset: buildbot_linux_1804]
utils/build-presets.ini:[preset: buildbot_linux_1610]
utils/build-presets.ini:[preset: buildbot_linux_1604]
utils/build-presets.ini:[preset: buildbot_linux_1510]
utils/build-presets.ini:[preset: buildbot_linux_1404]
utils/build-presets.ini:[preset: buildbot_linux,smoketest]
utils/build-presets.ini:[preset: buildbot_linux_1404_no_lldb]
utils/build-presets.ini:[preset: buildbot_linux_armv7]
utils/build-presets.ini:[preset: buildbot_incremental_linux_base]
utils/build-presets.ini:[preset: buildbot_incremental_linux]
utils/build-presets.ini:[preset: buildbot_incremental_linux,long_test]
utils/build-presets.ini:[preset: buildbot_incremental_linux,llvm-only]
utils/build-presets.ini:[preset: buildbot_incremental_linux,asan]
utils/build-presets.ini:[preset: buildbot_incremental_linux,lsan,tools=RDA,stdlib=RDA,test=no]
utils/build-presets.ini:[preset: buildbot_incremental_linux,lsan,tools=RDA,stdlib=DA,test=no]

[asowani]

What is the best way to test preset? I tried using command "utils/build-script --preset=buildbot_incremental_linux" in my VM and it worked fine. However, when I specified this argument, it did not pick up "tools=RA,stdlib=RD" and hence worked in my VM. However, in case of Jenkins, looks like it tries to match entire string with the one specified in build-presets.ini file. I am not very clear about the interpretation of R/D/A but I guess none of these are required for ppc64le. So I guess ""preset": "buildbot_incremental_linux"" would suffice in ppc64le_16_04.json file.

[shahmishal]

@asowani Thats the correct way of testing it.

Verify preset builds on the server:

1. Clone Swift git clone https://github.com/apple/swift.git
2. Clone all other repositories ./swift/utils/update-checkout --scheme --clone
3. Build + Test ./swift/utils/build-script --preset=