[Windows] Restrict searchpath of dbghelp.dll to System32 (#90520)

LoadLibraryW will lookup dlls in user directories if its search path is
left unrestricted. This is a security vulnerability as one can name a
shared library the same as that of a system dll in order to run
arbitrary code when the shared library is loaded from the path in a user
directory. This change modifies it to only search within sys32 when
loading dbghelp.dll.