[Support] [Windows] Stop redefining _WIN32_IE (#102307)

This was added in 181fd8c, where the
shlobj.h header was taken into use. The shlobj.h header does have some
APIs conditionally visible based on the _WIN32_IE define, but none of
the calls added in that commit seem to need any specific version.

fd6cb64 and
6b129bd further bumped the version it
is set to, while the latter also added a FIXME to check whether it still
is needed.

It doesn't seem to be needed currently; the code currently builds fine
without this define, both with mingw-w64 and MSVC.

Additionally, to show that the value of _WIN32_IE doesn't seem to be
relevant to our builds these days - if the current define is changed to
hardcode _WIN32_IE to an ancient value like 0x0400, our code still
builds fine, both with mingw-w64 and MSVC. Therefore, overriding this
define no longer seem to be relevant.

Author: mstorsjo

llvm/include/llvm/Support/Windows/WindowsSupport.h

@@ -23,11 +23,9 @@
 
 // mingw-w64 tends to define it as 0x0502 in its headers.
 #undef _WIN32_WINNT
-#undef _WIN32_IE
 
 // Require at least Windows 7 API.
 #define _WIN32_WINNT 0x0601
-#define _WIN32_IE    0x0800 // MinGW at it again. FIXME: verify if still needed.
 #define WIN32_LEAN_AND_MEAN
 #ifndef NOMINMAX
 #define NOMINMAX