PR13838: Added basic floating point support to systemtap

PR13838: Added basic floating point support to systemtap

runtime/softfloat.*: including floating point type definition
runtime/softfloat/*: all other required auxiliary functions

These are from https://github.com/ucb-bar/berkeley-softfloat-3
by John R. Hauser, thanks!

tapset/floatingpoing.stp: including fp conversion, fp arithmetic and
comparison functions testsuite/buildok/floatingpoint.stp: including testcase
for corresponding floatingpoing tapset main.cxx: changed sdt_benchmark part
of code for a demo of extracting floating point

Systemtap support 64 bit floating pounint (double type) under ieee754.
Conversions(fp <-> long, fp <-> string), arithmetic(add, sub, div, mul, sqrt)
and comparison between fp(less than, less than or equal to, equal) are
supported, corresponding tapset functions and test case are provided as well.