Disable library grade detection when building Mercury itself.

Library grade detection causes the library installation for the csharp grade
(and probably any grades that use mmc --make) to fail.  (There is likely
a better solution than this, e.g. making --no-mercury-stdlib-dir imply
--no-detect-libgrades, but the handling of command line options in this
part of the compiler is pretty convoluted, so I will look into that
separately.)

browser/MDB_FLAGS.in:
compiler/COMP_FLAGS.in:
deep_profiler/DEEP_FLAGS.in:
library/LIB_FLAGS.in:
mdbcomp/MDBCOMP_FLAGS.in:
mfilterjavac/MFILTERJAVAC_FLAGS.in:
profiler/PROF_FLAGS.in:
slice/SLICE_FLAGS.in:
ssdb/SSDB_FLAGS.in:
	As above.