Bug 1623073 - Properly prefix ICU data symbol with GNU as when needed; r=froydnj

Differential Revision: https://phabricator.services.mozilla.com/D67148

--HG--
extra : moz-landing-system : lando

config/external/icu/data/icudata_gas.S

@@ -5,8 +5,13 @@
 #if defined(__linux__) && defined(__ELF__)
 .section .note.GNU-stack,"",%progbits
 #endif
-.global ICU_DATA_SYMBOL
+#ifdef PREFIX
+#  define DATA_SYMBOL _##ICU_DATA_SYMBOL
+#else
+#  define DATA_SYMBOL ICU_DATA_SYMBOL
+#endif
+.global DATA_SYMBOL
 .data
 .balign 16
-ICU_DATA_SYMBOL:
+DATA_SYMBOL:
         .incbin ICU_DATA_FILE