pw_build: Add -O and -g flags to rustflags

-O and -g flags specified through GN toolchains were missing from
rustflags.

Change-Id: Ifb3aa5c2967fe4b717de72f1a8ca7b9d0d40313e
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/236392
Reviewed-by: Erik Gilling <[email protected]>
Docs-Not-Needed: Jiacheng Lu <[email protected]>
Commit-Queue: Jiacheng Lu <[email protected]>
Lint: Lint 🤖 <[email protected]>

pw_build/BUILD.gn

@@ -43,38 +43,38 @@ config("colorize_output") {
 config("debugging") {
   # Enable debug symbol generation. This has no effect on final code size.
   cflags = [ "-g" ]
-  rustflags = [ "-Clink-arg=-g" ]
+  rustflags = cflags + [ "-Clink-arg=-g" ]
 }
 
 config("extra_debugging") {
   # Include things like macro expansion in debug info.
   cflags = [ "-g3" ]
-  rustflags = [ "-Clink-arg=-g3" ]
+  rustflags = cflags + [ "-Clink-arg=-g3" ]
 }
 
 # Optimization levels
 config("optimize_debugging") {
   cflags = [ "-Og" ]
   ldflags = cflags
-  rustflags = [ "-Clink-arg=-Og" ]
+  rustflags = cflags + [ "-Clink-arg=-Og" ]
 }
 
 config("optimize_speed") {
   cflags = [ "-O2" ]
   ldflags = cflags
-  rustflags = [ "-Clink-arg=-O2" ]
+  rustflags = cflags + [ "-Clink-arg=-O2" ]
 }
 
 config("optimize_more_speed") {
   cflags = [ "-O3" ]
   ldflags = cflags
-  rustflags = [ "-Clink-arg=-O3" ]
+  rustflags = cflags + [ "-Clink-arg=-O3" ]
 }
 
 config("optimize_size") {
   cflags = [ "-Os" ]
   ldflags = cflags
-  rustflags = [ "-Clink-arg=-Os" ]
+  rustflags = cflags + [ "-Clink-arg=-Os" ]
 }
 
 config("enable_clang_fixed_point_types") {