Capture GCC warning group as flycheck error id

flycheck.el

@@ -6378,8 +6378,6 @@ warnings."
 Requires GCC 4.8 or newer.  See URL `https://gcc.gnu.org/'."
   :command ("gcc"
             "-fshow-column"
-            "-fno-diagnostics-show-option" ; Do not show the corresponding
-                                        ; warning group
             "-iquote" (eval (flycheck-c/c++-quoted-include-directory))
             (option "-std=" flycheck-gcc-language-standard concat)
             (option-flag "-pedantic" flycheck-gcc-pedantic)
@@ -6410,7 +6408,8 @@ Requires GCC 4.8 or newer.  See URL `https://gcc.gnu.org/'."
    (info line-start (or "<stdin>" (file-name)) ":" line ":" column
          ": note: " (message) line-end)
    (warning line-start (or "<stdin>" (file-name)) ":" line ":" column
-            ": warning: " (message) line-end)
+            ": warning: " (message (one-or-more (not (any "\n["))))
+            (optional "[" (id (one-or-more not-newline)) "]") line-end)
    (error line-start (or "<stdin>" (file-name)) ":" line ":" column
           ": " (or "fatal error" "error") ": " (message) line-end))
   :error-filter

test/flycheck-test.el

@@ -2771,10 +2771,11 @@ evaluating BODY."
   (let ((flycheck-disabled-checkers '(c/c++-clang c/c++-cppcheck)))
     (flycheck-ert-should-syntax-check
      "language/c_c++/warning.c" 'c-mode
-     '(5 10 warning "unused variable 'unused'" :checker c/c++-gcc)
+     '(5 10 warning "unused variable 'unused'"
+         :id "-Wunused-variable" :checker c/c++-gcc)
      '(7 15 warning "comparison between signed and unsigned integer expressions"
-         :checker c/c++-gcc)
-     '(8 7 warning "#warning" :checker c/c++-gcc))))
+         :id "-Wsign-compare" :checker c/c++-gcc)
+     '(8 7 warning "#warning" :id "-Wcpp" :checker c/c++-gcc))))
 
 (flycheck-ert-def-checker-test c/c++-gcc (c c++) included-file-error
   (let ((flycheck-gcc-include-path '("./include"))