Document the building macros.

# MAKEOVERRIDES= effectively "equalizes" GNU-ish and SysV-ish make flavors,

# which in turn eliminates ambiguities in variable treatment with -e.

# BUILD_CMD is a generic macro to build a given target in a given

# subdirectory.  The target must be given through the shell variable

# `target' and the subdirectory to build in must be given through `dir'.

# This macro shouldn't be used directly, use RECURSIVE_BUILD_CMD or

# BUILD_ONE_CMD instead.

#

# BUILD_ONE_CMD is a macro to build a given target in a given

# subdirectory if that subdirectory is part of $(DIRS).  It requires

# exactly the same shell variables as BUILD_CMD.

#

# RECURSIVE_BUILD_CMD is a macro to build a given target in all

# subdirectories defined in $(DIRS).  It requires that the target

# is given through the shell variable `target'.

BUILD_CMD=  if [ -d "$$dir" ]; then \

	    (	cd $$dir && echo "making $$target in $$dir..." && \

		$(CLEARENV) && $(MAKE) -e $(BUILDENV) TOP=.. DIR=$$dir $$target \