util/ide-config.sh: Fix invalid cStandard c18

I'm not sure what changed, but VSCode doesn't recognize "c18".
The next best option is c17 or gnu17.

The original change to c18 was
commit 971e1b069f.

BRANCH=none
BUG=none
TEST=./util/ide-config.sh vscode all:RW all:RO | tee .vscode/c_cpp_properties.json
     # Check that VSCode is happy with gnu17 in
     # .vscode/c_cpp_properties.json.

Signed-off-by: Craig Hesling <hesling@chromium.org>
Change-Id: I6797898dc7b546f805de43e07457a98ba22cc9ad
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2593917
Commit-Queue: Jett Rink <jettrink@chromium.org>
Reviewed-by: Jett Rink <jettrink@chromium.org>

util/ide-config.sh

@@ -231,7 +231,9 @@ vscode() {
 				echo '"compilerPath": "/usr/bin/arm-none-eabi-gcc",'
 				# echo '"compilerArgs": [],'
 				# The macro __STDC_VERSION__ is 201710L, which corresponds to c18.
-				echo '"cStandard": "c18",'
+				# VSCode doesn't have a C18 option, so go with C17. Since we seem
+				# to use a lot of GNUC features, let's go with gnu17 instead of c17.
+				echo '"cStandard": "gnu17",'
 				# echo '"cppStandard": "c++17",'
 				echo '"intelliSenseMode": "gcc-x64"'
 			} | {