Compiling postgresql with profiling

Defining CUSTOM_LDFLAGS in Makefile.custom does not have any
effect on the compilation. I found that LDFLAGS is hardcoded
in Makefile.global. Perhaps it would be a good idea to change
this? I had to edit Makefile.global and add '-pg' to LDFLAGS
manually.

I thought it was about time to run a profile on the backend...

/* m */