Add script for determining the set of symbols to export from a library. * build-aux/declared.sh: New file, from GNU libunistring. * doc/lib-symbol-visibility.texi (Exported Symbols of Shared Libraries): Mention it.

# Run "make check" to ensure that the code passes some simple tests,
# usually (always?) not involving compilation.
all:

check:
	./t-idcache