makefile: add test to verify modern OpenMP implementation

Older OpenMP implementations don't allow unsigned iterators.

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
makefile: make OpenMP test check for 'atomic update' support

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
GNUmakefile: support $(BIN)

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
common.mk: check for compiler support for certain flags

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
submodules: improve compiler support

Signed-off-by: Steven Noonan <steven@uplinklabs.net>