GCC: Add the -u flag to keep the main() symbol

This fixes the undefined reference to 'main' that arose after adding
the "-flto" flag to compilation.

This was the case for combined "-Wl,--wrap,main" and "-flto" flags.

Author: Filip Jagodzinski

tools/profiles/develop.json

@@ -12,7 +12,7 @@
         "ld": ["-Wl,--gc-sections", "-Wl,--wrap,main", "-Wl,--wrap,_malloc_r",
                "-Wl,--wrap,_free_r", "-Wl,--wrap,_realloc_r", "-Wl,--wrap,_memalign_r",
                "-Wl,--wrap,_calloc_r", "-Wl,--wrap,exit", "-Wl,--wrap,atexit",
-               "-Wl,-n"]
+               "-Wl,-n", "-u main"]
     },
     "ARMC6": {
         "common": ["-c", "--target=arm-arm-none-eabi", "-mthumb", "-Os",

tools/profiles/release.json

@@ -12,7 +12,7 @@
         "ld": ["-Wl,--gc-sections", "-Wl,--wrap,main", "-Wl,--wrap,_malloc_r",
                "-Wl,--wrap,_free_r", "-Wl,--wrap,_realloc_r", "-Wl,--wrap,_memalign_r",
                "-Wl,--wrap,_calloc_r", "-Wl,--wrap,exit", "-Wl,--wrap,atexit",
-               "-Wl,-n"]
+               "-Wl,-n", "-u main"]
     },
     "ARMC6": {
         "common": ["-c", "--target=arm-arm-none-eabi", "-mthumb", "-Oz",