RFR: JDK-8142907 Integration of minor fixes from the build-infra project

[Magnus Ihse Bursie]

The build-infra project has collected a number of minor fixes and 
changes during the new hotspot build development. It's a mix of code 
cleanup and new capabilities.

Not all of these new features are immediately beneficial to the JDK, but 
they will be needed for the upcoming new Hotspot build, and it will not 
hurt to have them in mainline. (In fact, it will tremendously help 
merging between mainline and build-infra.)

The fix addresses these issues:

In general:
* Break out hotspot configuration into hotspot.m4
* Long link lines uses @-files
* Consistently use -Wl instead of -Xlinker
* Improve clang on linux compilation
* Set shared library name explicitely on solaris
* Set correct shared library flag on Windows (-dll)
* Consistency fixes for build toolchain
* Bring compare script up to date
* General code/whitespace cleanup
* Additional functionality in MakeBase

In NativeCompilation.gmk:
* More efficient vardeps for per-file CFLAGS
* Fewer shell executions (means better performance on Windows)
* EXCLUDE_PATTERN and EXTRA_OBJECT_FILES
* Debug symbols on macosx (disabled for existing code to keep current 
behavior)

Enabling debug info on macosx on existing jdk should be treated in a 
follow-up bug.
Bug: https://bugs.openjdk.java.net/browse/JDK-8142907
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8142907-build-infra-integration-closed/webrev.01

(It turned out that WebRev could not at the same time include files from 
multiple repos and track the history of a "hg cp":ied file. So I created 
an alternative revision here:
http://cr.openjdk.java.net/~ihse/JDK-8142907-build-infra-integration-closed/webrev.02/

It does not include the jdk files, but hotspot.m4 might be easier to 
understand)

/Magnus