microsoft/compiler: Enable dxil_nir.h to be included from C++

Reviewed-by: Bill Kristiansen <billkris@microsoft.com>
Acked-by: Michael Tang <tangm@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9846>

src/microsoft/compiler/dxil_nir.h

@@ -28,6 +28,10 @@
 #include "nir.h"
 #include "nir_builder.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 bool dxil_nir_lower_8bit_conv(nir_shader *shader);
 bool dxil_nir_lower_16bit_conv(nir_shader *shader);
 bool dxil_nir_lower_x2b(nir_shader *shader);
@@ -47,4 +51,8 @@ build_load_ubo_dxil(nir_builder *b, nir_ssa_def *buffer,
                     nir_ssa_def *offset, unsigned num_components,
                     unsigned bit_size);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* DXIL_NIR_H */