RFR: Only include fpu_control.h on 32-bit x86

[Mikael Vidstedt]

os_linux_x86_.cpp has some code to set/update/tickle the fpu control word. The code makes use of functions from the fpu_control.h header, but is only used on 32-bit x86. musl doesn’t have the fpu_control.h header file.

This change adds a conditional include guard to only include the fpu_control.h on 32-bit x86 (!AMD64), which matches the guards used in the places further down in the file where the functionality is actually used.

http://cr.openjdk.java.net/~mikael/webrevs/portola/fpucontrol/webrev.00/hotspot/webrev/

Cheers,
Mikael