cmake throwing ICONV_LIBRARIES not found error

[vishless]

Trying to install zxing_cpp gem in windows with the following command

gem install zxing_cpp

cmake complains that some environment variables (ICONV_LIBRARIES) are missing.

Environment:
Windows 10
ruby 2.5.7
zxing_cpp 0.1.1
cmake 3.20.5

Here's the complete log of the gem build:

CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
ICONV_LIBRARIES (ADVANCED)

C:\Users\viprasant>gem install zxing_cpp
Temporarily enhancing PATH for MSYS/MINGW...
Building native extensions. This could take a while...
ERROR:  Error installing zxing_cpp:
        ERROR: Failed to build gem native extension.

    current directory: C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/zxing_cpp-0.1.1/ext/zxing
C:/Ruby25-x64/bin/ruby.exe -r ./siteconf20210812-12952-1wi1uye.rb extconf.rb
CMake Deprecation Warning at CMakeLists.txt:6 (cmake_minimum_required):
  Compatibility with CMake < 2.8.12 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.


CMake Warning at CMakeLists.txt:88 (message):
  Not building testrunner, because CppUnit is missing


CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
ICONV_LIBRARIES (ADVANCED)
    linked by target "libzxing" in directory C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/zxing_cpp-0.1.1/ext/zxing/zxing-cpp

CMake Generate step failed.  Build files cannot be regenerated correctly.
make: *** No targets specified and no makefile found.  Stop.
creating Makefile

current directory: C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/zxing_cpp-0.1.1/ext/zxing
make "DESTDIR=" clean

current directory: C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/zxing_cpp-0.1.1/ext/zxing
make "DESTDIR="
generating zxing-x64-mingw32.def
compiling zxing.cc
linking shared-object zxing/zxing.so
x86_64-w64-mingw32-g++.exe: error: C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/zxing_cpp-0.1.1/ext/zxing/zxing-cpp/build/libzxing.a: No such file or directory
make: *** [Makefile:259: zxing.so] Error 1

make failed, exit code 2

Gem files will remain installed in C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/zxing_cpp-0.1.1 for inspection.
Results logged to C:/Ruby25-x64/lib/ruby/gems/2.5.0/extensions/x64-mingw32/2.5.0/zxing_cpp-0.1.1/gem_make.out