RFR (XS): 8144881: Various fixes to linux/sparc

[Mikael Vidstedt]

Please review this small change which fixes a handful of places which 
currently lead to build failures on linux/sparc. The changes are all 
relatively straightforward and come in a few different flavors:

* Incorrect format specifiers
* "reaches end of function returning value"
* wrong type name (sigcontext_t -> struct sigcontext)
* wrong variable name (addr -> pc)

Bug: https://bugs.openjdk.java.net/browse/JDK-8144881
Webrev: http://cr.openjdk.java.net/~mikael/webrevs/8144881/webrev.00/webrev/

Cheers,
Mikael