The WebKit build is configured to use ccache if it is found on the system. This is intended to speed up builds, but the Windows build will fail if the Cygwin ccache is found. The error message is something like:

$ gradle --info -PCOMPILE_WEBKIT=true
...
+ cmake -DPORT="Java" -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DCMAKE_BUILD_TYPE=Release -G Ninja -DSHOW_BINDINGS_GENERATION_PROGRESS=1 -DDEVELOPER_MODE=ON -DENABLE_TOOLS=1 -DCMAKE_C_COMPILER='VS2019INSTALLDIR/VC/bin/x64/cl.exe' -DJAVAFX_RELEASE_VERSION=18 ...
"...\modules\javafx.web\src\main\native"
-- Enabling ccache: Setting ccache prefix for compiler.
...
[440/4683] Building CXX object Source\ThirdParty\icu\CMakeFiles\icui18n.dir\source\i18n\astro.cpp.obj
FAILED: Source/ThirdParty/icu/CMakeFiles/icui18n.dir/source/i18n/astro.cpp.obj
C:/cygwin64/bin/ccache.exe VS2019INSTALLDIR\VC\bin\x64\cl.exe /nologo /TP -DBUILDING_JAVA__=1 -DBUILDING_WITH_CMAKE=1 -DDATA_DIR=\"share\" -DHAVE_CONFIG_H=1 -DHAVE_DLOPEN=0 -DICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_STATIC -DLIB_ICU_I18N_STATIC -DNOMINMAX -DUCONFIG_ONLY_HTML_CONVERSION=1 -DUNICODE -DU_CHARSET_IS_UTF8=1 -DU_ENABLE_DYLOAD=0 -DU_I18N_IMPLEMENTATION -DU_STATIC_IMPLEMENTATION -DWINVER=0x601 -D_CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES=1 -D_CRT_SECURE_NO_WARNINGS -D_HAS_EXCEPTIONS=0 -D_UNICODE -D_WINDOWS -D_WINSOCKAPI_="" -Imodules\javafx.web\src\main\native\Source\ThirdParty\icu\source\common -Imodules\javafx.web\src\main\native\Source\ThirdParty\icu\source\i18n /W4 /DWIN32 /D_WINDOWS /GR- /EHs- /EHc- /MD /O2 /Ob2 /DNDEBUG /wd4018 /wd4060 /wd4068 /wd4100 /wd4127 /wd4146 /wd4189 /wd4201 /wd4244 /wd4245 /wd4251 /wd4275 /wd4267 /wd4305 /wd4309 /wd4312 /wd4324 /wd4389 /wd4456 /wd4457 /wd4458 /wd4459 /wd4505 /wd4611 /wd4646 /wd4701 /wd4702 /wd4706 /wd4715 /wd4722 /wd4838 /wd4840 /wd4996 /wd5205 /Zi /GS /EHa- /EHc- /EHs- /fp:except- /analyze- /bigobj /utf-8 /validate-charset /Oy- /GR /wd4005 -std:c++17 /showIncludes /FoSource\ThirdParty\icu\CMakeFiles\icui18n.dir\source\i18n\astro.cpp.obj /FdSource\ThirdParty\icu\CMakeFiles\icui18n.dir\icui18n.pdb /FS -c modules\javafx.web\src\main\native\Source\ThirdParty\icu\source\i18n\astro.cpp
ccache: FATAL: Could not find compiler "VS2019INSTALLDIR\VC\bin\x64\cl.exe" in PATH
[441/4683] Building CXX object Source\ThirdParty\icu\CMakeFiles\icui18n.dir\source\i18n\anytrans.cpp.obj
FAILED: Source/ThirdParty/icu/CMakeFiles/icui18n.dir/source/i18n/anytrans.cpp.obj