Remove non-compiling hash_value function

[nirinchev]

What, How & Why?

stdext::hash_value doesn't seem to exist on Windows and we already define a hashing function in

realm-core/src/external/s2/s2cellid.h

Lines 498 to 504 in e079865

	HASH_NAMESPACE_START
	template<> struct hash<S2CellId> {
	size_t operator()(S2CellId const& id) const {
	return static_cast<size_t>(id.id() >> 32) + static_cast<size_t>(id.id());
	}
	};
	HASH_NAMESPACE_END

[kiburtse]

Weird that it didn't trigger our CI, and also worked for me on windows. Could you post the error which you've hit? Just for reference. Function is indeed not needed. We may probably clean a few more of them.

[nirinchev]

This is the incremental build output when I build from the feature/geo.. branch:

-- Selecting Windows SDK version 10.0.22621.0 to target Windows 10.0.
-- CMake version: 3.24.202208181-MSVC_2
Dependencies: PACKAGE_NAME=realm-core;VERSION=13.9.0;OPENSSL_VERSION=3.0.8;WIN32_ZLIB_VERSION=1.2.13;MDBREALM_TEST_SERVER_TAG=2023-03-16
-- Configuring done
-- Generating done
-- Build files have been written to: C:/work/dotnet/wrappers/cmake/Windows/Debug-ARM64
MSBuild version 17.4.0+18d5aef85 for .NET Framework
  Checking Build System
  Bid.vcxproj -> C:\work\dotnet\wrappers\cmake\Windows\Debug-ARM64\realm-core\src\external\IntelRDFPMathLib20U2\Bid.dir
  \Debug\Bid.lib
  s2cellid.cc
C:\work\dotnet\wrappers\realm-core\src\external\s2\s2cellid.cc(525,27): error C2039: 'hash_value': is not a member of 'stdext' [C:\work\dotnet\wrappers\cmake\Windows\Debug-ARM64\realm-core\src\external\s2\s2geometry.vcxproj]
C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.34.31933\include\iterator(1426,1): message : see declaration of 'stdext' [C:\work\dotnet\wrappers\cmake\Windows\Debug-ARM64\realm-core\src\external\s2\s2geometry.vcxproj]
C:\work\dotnet\wrappers\realm-core\src\external\s2\s2cellid.cc(525,37): error C2988: unrecognizable template declaration/definition [C:\work\dotnet\wrappers\cmake\Windows\Debug-ARM64\realm-core\src\external\s2\s2geometry.vcxproj]
C:\work\dotnet\wrappers\realm-core\src\external\s2\s2cellid.cc(525,37): error C2143: syntax error: missing ';' before '<' [C:\work\dotnet\wrappers\cmake\Windows\Debug-ARM64\realm-core\src\external\s2\s2geometry.vcxproj]
C:\work\dotnet\wrappers\realm-core\src\external\s2\s2cellid.cc(525,37): error C2059: syntax error: '<' [C:\work\dotnet\wrappers\cmake\Windows\Debug-ARM64\realm-core\src\external\s2\s2geometry.vcxproj]
C:\work\dotnet\wrappers\realm-core\src\external\s2\s2cellid.cc(525,68): error C2143: syntax error: missing ';' before '{' [C:\work\dotnet\wrappers\cmake\Windows\Debug-ARM64\realm-core\src\external\s2\s2geometry.vcxproj]
C:\work\dotnet\wrappers\realm-core\src\external\s2\s2cellid.cc(525,68): error C2447: '{': missing function header (old-style formal list?) [C:\work\dotnet\wrappers\cmake\Windows\Debug-ARM64\realm-core\src\external\s2\s2geometry.vcxproj]

Not sure if my MSBuild version is different from yours or if it's because I'm building this for Arm.