build system ignores --with-icu= option

[sergey@…]

Configured as:

./bootstrap.sh --with-icu --with-icu=/opt/icu4c-52.1

I can see that line in project-config.jam exists:

path-constant ICU_PATH : /opt/icu4c-52.1 ;

But when I run ./b2 -a it reports:

• has_icu builds : yes (cached)

...

• Boost.Locale needs either iconv or ICU library to be built.

(repeated many times)

[Steven Watanabe]

It looks like Boost.Regex works when ICU_PATH is defined using path-constant, but Boost.Locale doesn't.