RFR(S): 8046818: Hotspot build system looking for sdt.h in the wrong place

[Mikael Vidstedt]

Please review the below fix.

When using a compiler which does not use the default "/" as system root 
the system headers are not picked up from /usr/include. This means that 
looking for sdt.h in /usr/include is not correct - even if the machine 
in question has that header file available it may still fail at compile 
time if the compiler doesn't have sdt.h in its system root.

gcc has a useful option (-print-sysroot) which prints the system root 
being used. I have not found any equivalent option for clang, so this 
fix will unfortunately not solve this problem when using clang. When we 
rewrite the Hotspot build system to use the new top level build system 
this can be solved in a better way.

Bug: https://bugs.openjdk.java.net/browse/JDK-8046818
Webrev: http://cr.openjdk.java.net/~mikael/webrevs/8046818/webrev.00/webrev/

Cheers,
Mikael