Why does the UWP toolchain use /WX- by default?

[ikas-mc]

Recently, I added a clang-cl toolchain for vcpkg UWP, but found that some libraries which previously compiled successfully now fail to build. After read the source, I found that the original UWP toolchain uses the /WX- flag by default. why is this flag set this way?

I noticed that x64-uwp is still officially supported by vcpkg. However, the libraries built for UWP may not be fully reliable or trustworthy

libxml2

clang-cl.exe   -DLIBXML_STATIC -DSYSCONFDIR=\"E:/dev/tools/vcpkg/packages/libxml2_x64-llvm-uwp-static-md/debug/etc\" 
-IE:\dev\tools\vcpkg\buildtrees\libxml2\x64-llvm-uwp-static-md-dbg 
-IE:\dev\tools\vcpkg\buildtrees\libxml2\src\v2.13.8-66cf7e0652.clean\include 
-imsvcF:\dev\space\cmake\mpv-deps-vcpkg\mpv-deps-builder\vcpkg_installed\x64-llvm-uwp-static-md\debug\include 
-imsvcF:\dev\space\cmake\mpv-deps-vcpkg\mpv-deps-builder\vcpkg_installed\x64-llvm-uwp-static-md\include 
/DWIN32 /D_WINDOWS /D_UNICODE /DUNICODE /DWINAPI_FAMILY=WINAPI_FAMILY_APP /D__WRL_NO_DEFAULT_LIB__ /nologo
 /Z7 /GS /Gd /Gm- /W3 /WX- /Zc:wchar_t /Zc:inline /Zc:forScope /fp:precise /Oy- /EHsc  /utf-8  -pedantic -Wall -Wextra -Wshadow -Wpointer-arith -Wcast-align -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes -Wno-long-long -Wno-format-extra-args /MDd /Od /RTC1  -MDd /showIncludes /FoCMakeFiles\LibXml2.dir\globals.c.obj /FdCMakeFiles\LibXml2.dir\LibXml2.pdb -c -- E:\dev\tools\vcpkg\buildtrees\libxml2\src\v2.13.8-66cf7e0652.clean\globals.c
FAILED: CMakeFiles/LibXml2.dir/globals.c.obj 

E:\dev\tools\vcpkg\buildtrees\libxml2\src\v2.13.8-66cf7e0652.clean\globals.c(730,5): error: call to undeclared function
      'UnregisterWait'; ISO C99 and later do not support implicit function declarations
      [-Wimplicit-function-declaration]
  730 |     UnregisterWait(gs->waitHandle);
      |     ^
E:\dev\tools\vcpkg\buildtrees\libxml2\src\v2.13.8-66cf7e0652.clean\globals.c(746,9): error: call to undeclared function
      'RegisterWaitForSingleObject'; ISO C99 and later do not support implicit function declarations
      [-Wimplicit-function-declaration]
  746 |     if (RegisterWaitForSingleObject(&waitHandle, threadHandle,

\cl.exe   -DLIBXML_STATIC -DSYSCONFDIR=\"E:/dev/tools/vcpkg/packages/libxml2_x64-uwp-static-md/debug/etc\" -IE:\dev\tools\vcpkg\buildtrees\libxml2\x64-uwp-static-md-dbg 
-IE:\dev\tools\vcpkg\buildtrees\libxml2\src\v2.13.8-66cf7e0652.clean\include 
-external:IE:\dev\tools\vcpkg\installed\x64-uwp-static-md\include 
-external:W0 /DWIN32 /D_WINDOWS /D_UNICODE /DUNICODE /DWINAPI_FAMILY=WINAPI_FAMILY_APP 
/D__WRL_NO_DEFAULT_LIB__ /nologo /Z7 /MP /GS /Gd /Gm- /W3 /WX- /Zc:wchar_t /Zc:inline /Zc:forScope /fp:precise /Oy- /EHsc  /utf-8  /MDd /Od /RTC1  -MDd /showIncludes /FoCMakeFiles\LibXml2.dir\globals.c.obj /FdCMakeFiles\LibXml2.dir\LibXml2.pdb /FS -c E:\dev\tools\vcpkg\buildtrees\libxml2\src\v2.13.8-66cf7e0652.clean\globals.c

E:\dev\tools\vcpkg\buildtrees\libxml2\src\v2.13.8-66cf7e0652.clean\globals.c(730): warning C4013: “UnregisterWait”
E:\dev\tools\vcpkg\buildtrees\libxml2\src\v2.13.8-66cf7e0652.clean\globals.c(746): warning C4013: “RegisterWaitForSingleObject