DMD release compiler flags when building with LDC

[Per Nordlöw]

Have anybody experimented with release compilation flags when 
building dmd with ldc?

I'm currently calling make as

make -f posix.mak \
     DFLAGS="-noboundscheck" \
     ENABLE_RELEASE=1 \
     ENABLE_LTO=1 \
     HOST_CXX=g++ \
     HOST_DMD=ldmd2

And I measure about a 20-25% drop in runtime compared to the 
standard released version of dmd.

Is profile guided optimization (PGO) worth a try?