[native-library] If a dllimport is specified with an absolute path, l…

…ook for it first

The unmanaged native library probing documentation says to try
absolute paths without variations

https://learn.microsoft.com/en-us/dotnet/core/dependency-loading/default-probing#unmanaged-native-library-probing

Manual backport of  dotnet#85255 to net6

src/mono/mono/metadata/native-library.c

@@ -518,11 +518,18 @@ netcore_probe_for_module (MonoImage *image, const char *file_name, int flags)
 	// TODO: this algorithm doesn't quite match CoreCLR, so respecting DLLIMPORTSEARCHPATH_LEGACY_BEHAVIOR makes little sense
 	// If the difference becomes a problem, overhaul this algorithm to match theirs exactly
 
+	gboolean probe_first_without_prepend = FALSE;
+
 #if defined(HOST_ANDROID)
 	// On Android, try without any path additions first. It is sensitive to probing that will always miss
 	// and lookup for some libraries is required to use a relative path
-	module = netcore_probe_for_module_variations (NULL, file_name, lflags);
+	probe_first_without_prepend = TRUE;
+#else
+	if (file_name != NULL && g_path_is_absolute (file_name))
+		probe_first_without_prepend = TRUE;
 #endif
+	if (module == NULL && probe_first_without_prepend)
+		module = netcore_probe_for_module_variations (NULL, file_name, lflags);
 
 	// Check the NATIVE_DLL_SEARCH_DIRECTORIES
 	for (int i = 0; i < pinvoke_search_directories_count && module == NULL; ++i)
@@ -537,13 +544,11 @@ netcore_probe_for_module (MonoImage *image, const char *file_name, int flags)
 		g_free (mdirname);
 	}
 
-#if !defined(HOST_ANDROID)
-	// Try without any path additions
-	if (module == NULL)
+	// Try without any path additions, if we didn't try it already
+	if (module == NULL && !probe_first_without_prepend)
 	{
 		module = netcore_probe_for_module_variations (NULL, file_name, lflags);
 	}
-#endif
 
 	// TODO: Pass remaining flags on to LoadLibraryEx on Windows where appropriate, see https://docs.microsoft.com/en-us/dotnet/api/system.runtime.interopservices.dllimportsearchpath?view=netcore-3.1