Revert "Change to use -O0 instead of -O1 in debug build. (#1949)" (#1957)

This reverts commit feee02ca61.

toolchain-linux.cmake

@@ -13,7 +13,7 @@ else()
 endif()
 
 if (NOT DEFINED ENV{CXXFLAGS})
-  set(CMAKE_CXX_FLAGS_DEBUG "-g -O0")
+  set(CMAKE_CXX_FLAGS_DEBUG "-g -O1")
   set(CMAKE_CXX_FLAGS_RELEASE "-O3")
 endif()
 
@@ -24,6 +24,6 @@ else()
 endif()
 
 if (NOT DEFINED ENV{CFLAGS})
-  set(CMAKE_C_FLAGS_DEBUG "-g -O0")
+  set(CMAKE_C_FLAGS_DEBUG "-g -O1")
   set(CMAKE_C_FLAGS_RELEASE "-O3")
 endif()