doc: add description for AFL_GCC_DISABLE_VERSION_CHECK

docs/env_variables.md

@@ -326,6 +326,11 @@ mode.
     [instrumentation/README.instrument_list.md](../instrumentation/README.instrument_list.md)
     for more information.
 
+    Setting `AFL_GCC_DISABLE_VERSION_CHECK=1` will disable the GCC plugin 
+    version check if the target GCC plugin differs from the system-installed
+    version, resolving issues caused by version mismatches between GCC and 
+    the plugin. 
+
     Setting `AFL_GCC_OUT_OF_LINE=1` will instruct afl-gcc-fast to instrument the
     code with calls to an injected subroutine instead of the much more efficient
     inline instrumentation.

src/afl-cc.c

@@ -2958,6 +2958,8 @@ static void maybe_usage(aflcc_state_t *aflcc, int argc, char **argv) {
         SAYF(
             "\nGCC Plugin-specific environment variables:\n"
             "  AFL_GCC_CMPLOG: log operands of comparisons (RedQueen mutator)\n"
+            "  AFL_GCC_DISABLE_VERSION_CHECK: disable GCC plugin version "
+            "control\n"
             "  AFL_GCC_OUT_OF_LINE: disable inlined instrumentation\n"
             "  AFL_GCC_SKIP_NEVERZERO: do not skip zero on trace counters\n"
             "  AFL_GCC_INSTRUMENT_FILE: enable selective instrumentation by "