Request for review (S) 6588413: Use -fvisibility=hidden for gcc compiles

[Coleen Phillimore]

Summary: Add option for gcc 4 and above, define JNIEXPORT and JNIIMPORT 
to visibility=default, add for jio_snprintf and others since 
-fvisibility=hidden overrides --version-script definitions.

Performance increases measured by Volker and Tom;

5% (JBB2005) and 2% (JVM98) on Linux/IA64 and 1,5% (JBB2005) and
0,5% (JVM98) on Linux/PPC64


on intel hardware:

   specjvm98              15      314.61      0.00    0.33 0.006          Yes
     javac                15      248.88      0.01    1.72 0.000          Yes
     jack                 15      294.44      0.01    1.38 0.000          Yes


open webrev at http://cr.openjdk.java.net/~coleenp/6588413/
bug link at http://bugs.sun.com/view_bug.do?bug_id=6588413

Tested with jmap for any serviceability impact, and tested hs_err_file 
decoding still works.

Thanks,
Coleen