RFR: JDK-8039426: gcc can target wrong instruction set when building JDK native code

[Erik Joelsson]

Hello,

Please review this small fix to CFLAGS when compiling with GCC on a 
32-bit system. Hotspot currently sets -march=i586 and the jdk libraries 
should do the same for consistency.

Bug: https://bugs.openjdk.java.net/browse/JDK-8039426
Webrev: http://cr.openjdk.java.net/~erikj/8039426/webrev.01/

/Erik