mlir: emit libMLIR.so for not-static host platforms

mlir piggybacks onto LLVM_BUILD_LLVM_DYLIB for determining if a
shared libMLIR.so is emitted. This also fixes build failures
in MLIR 20+ where tablegen'd files aren't generated.

In file included from /build/mlir-src-21.0.0-unstable-2025-03-09/mlir/include/mlir/IR/UseDefLists.h:16,
                 from /build/mlir-src-21.0.0-unstable-2025-03-09/mlir/include/mlir/IR/Value.h:17,
                 from /build/mlir-src-21.0.0-unstable-2025-03-09/mlir/include/mlir/IR/BlockSupport.h:16,
                 from /build/mlir-src-21.0.0-unstable-2025-03-09/mlir/include/mlir/IR/OperationSupport.h:18,
                 from /build/mlir-src-21.0.0-unstable-2025-03-09/mlir/include/mlir/IR/Dialect.h:17,
                 from /build/mlir-src-21.0.0-unstable-2025-03-09/mlir/tools/mlir-lsp-server/mlir-lsp-server.cpp:9:
/build/mlir-src-21.0.0-unstable-2025-03-09/mlir/include/mlir/IR/Location.h:145:10: fatal error: mlir/IR/BuiltinLocationAttributes.h.inc: No such file or directory
  145 | #include "mlir/IR/BuiltinLocationAttributes.h.inc"
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.

Author: picostove

pkgs/development/compilers/llvm/common/mlir/default.nix

@@ -61,6 +61,7 @@ stdenv.mkDerivation rec {
     "-DLLVM_ENABLE_DUMP=ON"
     "-DLLVM_TABLEGEN_EXE=${buildLlvmTools.tblgen}/bin/llvm-tblgen"
     "-DMLIR_TABLEGEN_EXE=${buildLlvmTools.tblgen}/bin/mlir-tblgen"
+    (lib.cmakeBool "LLVM_BUILD_LLVM_DYLIB" (!stdenv.hostPlatform.isStatic))
   ] ++ lib.optionals stdenv.hostPlatform.isStatic [
     # Disables building of shared libs, -fPIC is still injected by cc-wrapper
     "-DLLVM_ENABLE_PIC=OFF"