add a way to specify alternative ICU libraries

Prior to Qt 5.8, configure had this option "-l" to explicitly specify a library name for linking. When we build Qt we use the option to rename Qt dlls and link with other libraries whose dlls were renamed as well.

Consider this configure command:
configure -qtlibinfix _xxx -platform win32-msvc2015 -opengl dynamic -sql-sqlite -icu -openssl-linked OPENSSL_LIBS="-lssleay32_xxx -llibeay32_xxx" -nomake examples -l sqlite3_xxx -l icudt_xxx -l icuin_xxx -l icuuc_xxx

where "xxx" is the suffix we use for renamed libraries.

With Qt 5.8 configure doesn't support "-l" option. May be there is another way to do this.