Merge branch 'mr/dmking/2001-add-s-sttefo' into 'master'

Add package Ada.Strings.Text_Formatters to embedded runtimes

See merge request eng/toolchain/bb-runtimes!302

Author: damaki

support/rts_sources/sources.py

@@ -599,6 +599,8 @@
             "libgnat/a-strunb.adb",
             "libgnat/a-sttebu.ads",
             "libgnat/a-sttebu.adb",
+            "libgnat/a-sttefo.ads",
+            "libgnat/a-sttefo.adb",
             "libgnat/a-stunau.ads",
             "libgnat/a-stunau.adb",
             "libgnat/a-stunha.ads",