JDK10/RFR(S): 8181868: Remove use of 'has_fast_fxtof()'

[Patric Hedlin]

Dear all,

I would like to ask for help to review the following change/update:

Issue:    https://bugs.openjdk.java.net/browse/JDK-8181868

Webrev:   http://cr.openjdk.java.net/~neliasso/phedlin/tr8181868/

Prerequisite: https://bugs.openjdk.java.net/browse/JDK-8172231


8181868: Remove use of 'has_fast_fxtof()'

     After JDK-8172231 we no longer support old SPARC HW lacking fast 
integer/floating-point conversion.


Testing:

     Mostly tested on JDK9 (jtreg/RBT/hotspot/tier0-comp).
     Testing on JDK10 (jtreg/RBT/hotspot/precheckin-comp).


Best regards,
Patric