Perl is case-sensitive; the module is IO::Prompt.
Additionally, your build log shows:
Test Summary Report
-------------------
t\01.dependencies.t (Wstat: 512 Tests: 2 Failed: 2)
Failed tests: 1-2
Non-zero exit status: 2
Files=4, Tests=3, 1 wallclock secs ( 0.06 usr + 0.03 sys = 0.09 CPU)
Result: FAIL
Failed 1/4 test programs. 2/3 subtests failed.
DCONWAY/IO-Prompt-0.997001.tar.gz
C:\strawberry\perl\bin\perl.exe ./Build test -- NOT OK
//hint// to see the cpan-testers results for installing this module, try:
reports DCONWAY/IO-Prompt-0.997001.tar.gz
Running Build install
make test had returned bad status, won't install without force
Failed during this command:
DCONWAY/IO-Prompt-0.997001.tar.gz : make_test NO
So, the module was not installed, which is the rest of the reason it is not found.