-fnothrow-opt

In case anybody ever wonders: -fnothrow-opt (treating "throw ()" like 
"noexcept", 
<https://gcc.gnu.org/onlinedocs/gcc-4.6.4/gcc/C_002b_002b-Dialect-Options.html#index-fnothrow_002dopt-148>; 
only available in GCC, not in Clang) would appear to not buy us anything 
for LO:  For one, it has zero effect on the generated code with 
-fno-enforce-eh-specs (enabled for --disable-dbgutil; only available in 
GCC, not in Clang).  For another, even if we used -fenforce-eh-specs, my 
GCC 4.9.2 --disable-dbgutil Linux master build would only shrink instdir 
by 20 bytes (from 1,817,288 to 1,817,268).