RFC: JEP 386 patch - minor cleanup

[Aleksei Voitylov]

Hi,

As JEP 386 is now Candidate [1] I'd like to request comments on the
patch [2] before moving the JEP to PTT and submitting for review
upstream. The patch is rebased to 59791:a22af2c3d969 and minor cleanup
of the changes from the original portola branch [3] was made.

Webrev [2]: http://cr.openjdk.java.net/~avoitylov/webrev.8247589
Original [3]: http://cr.openjdk.java.net/~avoitylov/webrev.portola

Build System, Toolchains:

- make/autoconf/build-aux/config.guess - replaced the "head -1 | cut
-f1" construct with sed to be slightly more robust
- make/autoconf/build-aux/config.sub - style brought in line with the
current file style
- make/autoconf/hotspot.m4 - HOTSPOT_SETUP_SA is no longer required
after JDK-8239450 [4]
- make/modules/jdk.jdwp.agent/Lib.gmk, make/test/JtregNativeJdk.gmk,
hotspot/share/gc/shared/genCollectedHeap.cpp - disabling GCC warnings
and modifying initialization is no longer required, Alpine Linux
toolchain is quite recent

Desktop:

- src/java.desktop/unix/native/libawt_xawt/xawt/XToolkit.c - changes are
present upstream and no longer required

HotSpot:

- src/hotspot/os/linux/os_linux.cpp - checks for MUSL can be made
static. Defined stub dlvsym for MUSL instead of dlvsym_if_available logic
- src/jdk.hotspot.agent/linux/native/libsaproc/ps_proc.c - using
strerror is cleaner and more portable, the code originally present there
is not thread-safe so it's ok to use it
- src/jdk.jdwp.agent/share/native/libjdwp/util.h - including a header
instead

java.base:

- src/java.base/linux/native/libnet/linux_close.c - made (SIGRTMAX - 2)
a define
- src/java.base/unix/native/libjava/childproc.c - suggest to skip this
for now. Also, if the OS does not handle scripts without shebang it
should not be emulated.

Tests:

- added method isBusyBox() to test/lib/jdk/test/lib/Platform.java
- added WB_InternalVMInfo method to hotspot/share/prims/whitebox.cpp for
better test handling
- refactored affected tests to cater for the above

Thanks,
-Aleksei

[1] https://openjdk.java.net/jeps/386
[2] http://cr.openjdk.java.net/~avoitylov/webrev.8247589
(https://bugs.openjdk.java.net/browse/JDK-8247589)
[3] http://cr.openjdk.java.net/~avoitylov/webrev.portola
[4] https://bugs.openjdk.java.net/browse/JDK-8239450