gcc-common.h: Update for GCC 10

Remove "params.h" include, which has been dropped in GCC 10.

Remove is_a_helper() macro, which is now defined in gimple.h, as seen
when running './scripts/gcc-plugin.sh g++ g++ gcc':

In file included from <stdin>:1:
./gcc-plugins/gcc-common.h:852:13: error: redefinition of ‘static bool is_a_helper<T>::test(U*) [with U = const gimple; T = const ggoto*]’
  852 | inline bool is_a_helper<const ggoto *>::test(const_gimple gs)
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from ./gcc-plugins/gcc-common.h:125,
                 from <stdin>:1:
/usr/lib/gcc/x86_64-redhat-linux/10/plugin/include/gimple.h:1037:1: note: ‘static bool is_a_helper<T>::test(U*) [with U = const gimple; T = const ggoto*]’ previously declared here
 1037 | is_a_helper <const ggoto *>::test (const gimple *gs)
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~

Add -Wno-format-diag to scripts/gcc-plugins/Makefile to avoid
meaningless warnings from error() formats used by plugins:

scripts/gcc-plugins/structleak_plugin.c: In function ‘int plugin_init(plugin_name_args*, plugin_gcc_version*)’:
scripts/gcc-plugins/structleak_plugin.c:253:12: warning: unquoted sequence of 2 consecutive punctuation characters ‘'-’ in format [-Wformat-diag]
  253 |   error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key);
      |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Signed-off-by: Frédéric Pierret (fepitre) <frederic.pierret@qubes-os.org>
Link: https://lore.kernel.org/r/20200407113259.270172-1-frederic.pierret@qubes-os.org
[kees: include -Wno-format-diag for plugin builds]
Signed-off-by: Kees Cook <keescook@chromium.org>

scripts/gcc-plugins/Makefile

@@ -4,6 +4,7 @@ GCC_PLUGINS_DIR := $(shell $(CC) -print-file-name=plugin)
 HOST_EXTRACXXFLAGS += -I$(GCC_PLUGINS_DIR)/include -I$(src) -std=gnu++98 -fno-rtti
 HOST_EXTRACXXFLAGS += -fno-exceptions -fasynchronous-unwind-tables -ggdb
 HOST_EXTRACXXFLAGS += -Wno-narrowing -Wno-unused-variable -Wno-c++11-compat
+HOST_EXTRACXXFLAGS += -Wno-format-diag
 
 $(obj)/randomize_layout_plugin.o: $(objtree)/$(obj)/randomize_layout_seed.h
 quiet_cmd_create_randomize_layout_seed = GENSEED $@

scripts/gcc-plugins/gcc-common.h

@@ -35,7 +35,9 @@
 #include "ggc.h"
 #include "timevar.h"
 
+#if BUILDING_GCC_VERSION < 10000
 #include "params.h"
+#endif
 
 #if BUILDING_GCC_VERSION <= 4009
 #include "pointer-set.h"
@@ -847,6 +849,7 @@ static inline gimple gimple_build_assign_with_ops(enum tree_code subcode, tree l
 	return gimple_build_assign(lhs, subcode, op1, op2 PASS_MEM_STAT);
 }
 
+#if BUILDING_GCC_VERSION < 10000
 template <>
 template <>
 inline bool is_a_helper<const ggoto *>::test(const_gimple gs)
@@ -860,6 +863,7 @@ inline bool is_a_helper<const greturn *>::test(const_gimple gs)
 {
 	return gs->code == GIMPLE_RETURN;
 }
+#endif
 
 static inline gasm *as_a_gasm(gimple stmt)
 {