linking against shaderc with CMake on Windows silently fails to produce meaningful output

The relevant contents of my CMakeLists.txt are:

```
#spirv-headers (NEEDED ONLY FOR SPIRV-TOOLS)
FetchContent_Declare(
spirv-headers
GIT_REPOSITORY git@github.com:KhronosGroup/SPIRV-Headers
GIT_TAG 1.5.3
EXCLUDE_FROM_ALL TRUE
)
FetchContent_MakeAvailable(spirv-headers)

#spirv-tools (NEEDED ONLY FOR SHADERC)
FetchContent_Declare(
spirv-tools
GIT_REPOSITORY git@github.com:KhronosGroup/SPIRV-Tools
GIT_TAG v2020.4
EXCLUDE_FROM_ALL TRUE
)
FetchContent_MakeAvailable(spirv-tools)

#glslang (NEEDED ONLY FOR SHADERC)
FetchContent_Declare(
glslang
GIT_REPOSITORY git@github.com:KhronosGroup/glslang
GIT_TAG 8.13.3743
EXCLUDE_FROM_ALL TRUE
)
FetchContent_MakeAvailable(glslang)

#shaderc
FetchContent_Declare(
shaderc
GIT_REPOSITORY git@github.com:google/shaderc.git
GIT_TAG v2020.2
EXCLUDE_FROM_ALL TRUE
)
#set(SHADERC_SKIP_INSTALL ON CACHE BOOL "" FORCE)
set(SHADERC_SKIP_TESTS ON CACHE BOOL "" FORCE)
FetchContent_MakeAvailable(shaderc)
target_link_libraries(gnomes PRIVATE shaderc)

```
(my executable name is "gnomes")

Running `cmake ..` in my project's `build` folder completes without error, but produces empty `_deps\shaderc-build` and `_deps\shaderc-src` folders. (`_deps\shaderc-subbuild` _does_ have various files, but neither `shaderc.lib` nor `shaderc.h`). The resulting Visual Studio .sln has my `gnomes` project, which attempts to link to `shaderc.lib` (no leading directory), and thus fails to link when it cannot find it.