Bug 530012 – [gtk] Update make_linux to simplify building of launcher.

Details:
- This makes make_linux.mak independent, i.e the following works:
  make -f make_linux.mak clean all
  It does so by assuming default values if they are not set by build.sh.
  However, build.sh still overrides values for backwards compatibility.
  I.e, I expect it will work fine with build servers.

- I migrated some linux-specific logic from build.sh to make_linux.mak
  * JAVA_HOME detection that I added earlier,
  * linux specific x86/x86_64 flags

- Added a new target: dev_build_install
  This can be invoked like:
    export DEV_ECLIPSE="your/eclipse"
    make -f make_linux.mak clean dev_build_install
  It builds the launcher/lib and then you can test the output in your
  dev eclipse. (see target for details.).

Test strategy:
I've done some very through testing, I'm pretty confident it shouldn't
break anything. I've accounted for x86/x86_64 differences.
I've added a print statement that prints info about variables:
$(info Input info: ....)
This line generates the same values for when you run build.sh as well
as when make_linux is invoked directly.

Produced eclipse and eclipse_xxxx.so work well.
Tested on Fedora 27, Wayland, gtk3.22, x86_64.

Bug: https://bugs.eclipse.org/bugs/show_bug.cgi?id=530012
Change-Id: I07ec8f453acd93d368e5e8f927fa65354da0f68b
Signed-off-by: Leo Ufimtsev <lufimtse@redhat.com>
4 files changed