zephyr: stop suppressing double-promotion warnings

The vendored C10 rsqrt helper now performs its calculation in float
precision, so Zephyr builds no longer need to disable this warning.

AI-assisted by Codex.

Change-Id: Ie4bfce34167645f8f330298678ee8b0b565d181d
Signed-off-by: Per Held <per.held@arm.com>

Author: perheld

zephyr/samples/hello-executorch/CMakeLists.txt

@@ -62,7 +62,7 @@ find_package(
 )
 
 set(CMAKE_CXX_FLAGS
-    "${CMAKE_CXX_FLAGS} -Wall -Wno-switch -Wno-float-conversion -Wno-double-promotion -ffunction-sections -fdata-sections"
+    "${CMAKE_CXX_FLAGS} -Wall -Wno-switch -Wno-float-conversion -ffunction-sections -fdata-sections"
 )
 
 # Always use selective build since embedded devices are resource constrained

zephyr/samples/mv2-ethosu/CMakeLists.txt

@@ -109,7 +109,7 @@ endif()
 project(executorch_mv2_ethosu)
 
 set(CMAKE_CXX_FLAGS
-    "${CMAKE_CXX_FLAGS} -Wall -Wno-switch -Wno-float-conversion -Wno-double-promotion -ffunction-sections -fdata-sections"
+    "${CMAKE_CXX_FLAGS} -Wall -Wno-switch -Wno-float-conversion -ffunction-sections -fdata-sections"
 )
 
 if(NOT DEFINED EXECUTORCH_DIR)