FindOpenMP fails if the build directory contains a colon character (:)

Minimal reproducer:

$ cat >CMakeLists.txt <<EOF
cmake_minimum_required(VERSION 3.16)
project(bug C)
find_package(OpenMP REQUIRED)
EOF
$ mkdir build:it
$ cd build:it
$ cmake ..
-- The C compiler identification is GNU 5.4.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
CMake Error at /usr/share/cmake-3.16/Modules/FindPackageHandleStandardArgs.cmake:146 (message):
  Could NOT find OpenMP_C (missing: OpenMP_C_FLAGS OpenMP_C_LIB_NAMES)
Call Stack (most recent call first):
  /usr/share/cmake-3.16/Modules/FindPackageHandleStandardArgs.cmake:393 (_FPHSA_FAILURE_MESSAGE)
  /usr/share/cmake-3.16/Modules/FindOpenMP.cmake:511 (find_package_handle_standard_args)
  CMakeLists.txt:3 (find_package)


-- Configuring incomplete, errors occurred!
See also "/home/arekfu/src/foo/build:it/CMakeFiles/CMakeOutput.log".
See also "/home/arekfu/src/foo/build:it/CMakeFiles/CMakeError.log".

Seen on CMake v3.16. CMake works fine if the build directory does not contain any colon characters.