New /* stable */ embedded-c pragma

[Felix Lu]

SystemTap translator now supports the /* stable */ embedded-c pragma 
for arity-0 functions. Functioncall results are now automatically stored 
to reduce overhead of duplicate calls(no need to explicitly store). 
Stable functioncalls inside loops are also pulled out by the optimizer. 

Example usage: https://sourceware.org/systemtap/examples/profiling/timeout.stp 

Runtime of stable tapset functioncalls reduced by 5-10% in general usage cases.