I got the following error using GHC 8.8.4, GitHub runner, Cabal 3.2.0.0 and Microsoft Windows Server 2019. The GitHub log is here:

2020-08-16T15:56:12.9629490Z [157 of 372] Compiling Agda.VersionCommit ( src\full\Agda\VersionCommit.hs, D:\a\agda\agda\dist-newstyle\build\x86_64-windows\ghc-8.8.4\Agda-2.6.2\build\Agda\VersionCommit.o )
2020-08-16T15:56:17.7635596Z 
2020-08-16T15:56:17.7636768Z Access violation in generated code when executing data at 0xffffffff96203590
2020-08-16T15:56:17.8198992Z 
2020-08-16T15:56:17.8200323Z  Attempting to reconstruct a stack trace...
2020-08-16T15:56:17.8200544Z 
2020-08-16T15:56:17.8200930Z    Frame	Code address
2020-08-16T15:56:17.8201219Z  * 0x461dab0	0xffffffff96203590
2020-08-16T15:56:17.8201439Z 
2020-08-16T15:56:18.1289630Z cabal.exe: Failed to build Agda-2.6.2. The build process terminated with exit
2020-08-16T15:56:18.1289917Z code 11

In the ticket #17926 (closed) was fixed an issue which generated a similar error. According to the information in that ticket, the fix was included in GHC 8.8.4.