microsoft/compiler: move c++ higher up

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7578>

src/microsoft/compiler/dxil_signature.h

@@ -28,6 +28,10 @@
 #include "nir.h"
 #include "util/string_buffer.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /* struct taken from DXILContainer
  * Enums values were replaced by uint32_t since the must occupy 32 bit
  */
@@ -131,10 +135,6 @@ struct dxil_psv_runtime_info_1 {
 struct dxil_mdnode;
 struct dxil_module;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 const struct dxil_mdnode *
 get_signatures(struct dxil_module *mod, nir_shader *s);