Fix conditions mismatch for gc-sections with lld

[illnyang]

Judging by the changes made in 410aa0a, gc-sections optimization should be enabled:

• for Unix targets
• when using lld newer than 12

Both conditions are checked when adding linker arguments, but only the latter condition is checked when writing the linker script. This PR adds the missing conditions.

Relevant code

runtime/src/coreclr/nativeaot/BuildIntegration/Microsoft.NETCore.Native.targets

Lines 319 to 323 in 410aa0a

	<ItemGroup Condition="'$(_targetOS)' != 'win' and '$(_IsApplePlatform)' != 'true'">
	<CustomLinkerArg Include="-Wl,--discard-all" />
	<CustomLinkerArg Include="-Wl,--gc-sections" Condition="'$(LinkerFlavor)' == '' or '$(LinkerFlavor)' == 'bfd' or '$(LinkerFlavor)' == 'lld'" />
	<CustomLinkerArg Include="-Wl,-T,&quot;$(NativeIntermediateOutputPath)sections.ld&quot;" Condition="'$(LinkerFlavor)' == 'lld' and '$(_LinkerVersion)' &gt; '12'" />
	</ItemGroup>

runtime/src/coreclr/nativeaot/BuildIntegration/Microsoft.NETCore.Native.targets

Lines 338 to 341 in 410aa0a

	<!-- write linker script for lld (13+) to retain the __modules section -->
	<WriteLinesToFile File="$(NativeIntermediateOutputPath)sections.ld" Lines="OVERWRITE_SECTIONS { __modules : { KEEP(*(__modules)) } }" Overwrite="true" Condition="'$(LinkerFlavor)' == 'lld' and '$(_LinkerVersion)' &gt; '12'" />

Reproduction steps

This discrepancy is not observable in standard use cases. However, overriding the relevant properties will result in a vague error message unrelated to the actual issue.

> dotnet publish -r win-x64 -p:PublishAot=true -p:LinkerFlavor=lld project.csproj

...\Microsoft.NETCore.Native.targets(364,156): error MSB4086: 
A numeric comparison was attempted on "$(_LinkerVersion)" that evaluates to "" instead of a number,
in condition "'$(LinkerFlavor)' == 'lld' and '$(_LinkerVersion)' > '12'".

Predictably, setting the _LinkerVersion property next will cause sections.ld file to be written but left unused:

> dotnet publish -r win-x64 -p:PublishAot=true -p:LinkerFlavor=lld -p:_LinkerVersion=13 project.csproj

Build succeeded (...)

> cat obj\Release\net8.0\win-x64\native\sections.ld

OVERWRITE_SECTIONS { __modules : { KEEP(*(__modules)) } }

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @MichalStrehovsky, @jkotas
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[MichalStrehovsky]

Thank you!

[MichalStrehovsky]

/ba-g known android timeouts