Fix rpath flags for boost library. #28588

git-svn-id: https://svn.sourceforge.jp/svnroot/molds/branches/automake@1705 1136aad2-a195-0410-b898-f5ea1d11b9d8
Use BUILDDIR variable to change build directory. #28588

git-svn-id: https://svn.sourceforge.jp/svnroot/molds/branches/automake@1706 1136aad2-a195-0410-b898-f5ea1d11b9d8