[foreign] RFR 8212049: Improve jextract usability

[Maurizio Cimadamore]

Hi,
quoting from the JBS issue:

"There are some low hanging fruits that could significantly improve 
usability of jextract:

1) auto excluding symbols not found with -l/-L
2) inferring rpath from -L/-l (e.g. -rpath:auto)
3) applying same header settings (e.g. rpath) to ALL headers being 
extracted, not just the explicitly provided ones
4) treat headers in the same folders as a 'unit' (even if in system 
folders), and ignore dependencies outside this unit

(3) and (4) are particularly important because right now we tend to have 
many subtle asymmetries between different header files being generated, 
depending on whether they are explicit/implicit and whether they live in 
system folders or not. This makes the jextract behaviour particularly 
hard to grasp."

This patch fixes all 1-4 (and additionally fixes a crash when libraries 
could not be loaded by the symbol checker enabled with -l and -L).

I've added (with help of Sundar many thanks!) tests for (1), (2), and 
(3) (and the crash issue). I also have test for (4), although is 
probably a bit limited (but better than nothing): I simply check that 
when extracting an header that depends on <stdio.h> we don't end up 
generating artifacts for stdio too.

Webrev:

http://cr.openjdk.java.net/~mcimadamore/panama/8212049_v3/webrev/

You might want to check any existing local tests you might have to make 
sure nothing is broken by these cha

Maurizio