That works.

$ tclsh
tclsh8.6 [/tmp] package require md4
1.0.6
tclsh8.6 [/tmp] ::md4::md4c hello
d7ËzyKÎ+rzÌbî'

So either the pkgIndex.tcl is missing a line for md4c, or the ineffective "package require md4c" should be changed/removed from