feat: add compiler config for not merging const sections

Probably GCC-13.x and on-wards uses "-fmerge-constants" to merge
the const section (string/floating-point) across compilation units.
This makes it difficult to properly analyze the size output of rodata
section across libraries, the merged section (big in size) is showed
across a single library.

The config option added here can help to disable this compiler behavior
and help to provide better size analysis. It can be used during
development phase only as it increases rodata section size.

CMakeLists.txt

@@ -134,6 +134,10 @@ if(CONFIG_COMPILER_OPTIMIZATION_ASSERTIONS_DISABLE)
     list(APPEND compile_definitions "-DNDEBUG")
 endif()
 
+if(CONFIG_COMPILER_NO_MERGE_CONSTANTS)
+    list(APPEND compile_options "-fno-merge-constants")
+endif()
+
 if(CONFIG_COMPILER_STACK_CHECK_MODE_NORM)
     list(APPEND compile_options "-fstack-protector")
 elseif(CONFIG_COMPILER_STACK_CHECK_MODE_STRONG)

Kconfig

@@ -496,6 +496,15 @@ mainmenu "Espressif IoT Development Framework Configuration"
             help
                 Stack smashing protection.
 
+        config COMPILER_NO_MERGE_CONSTANTS
+            bool "Disable merging const sections"
+            depends on IDF_TOOLCHAIN_GCC
+            help
+                Disable merging identical constants (string/floating-point) across compilation units.
+                This helps in better size analysis of the application binary as the rodata section
+                distribution is more uniform across libraries. On downside, it may increase
+                the binary size and hence should be used during development phase only.
+
         config COMPILER_WARN_WRITE_STRINGS
             bool "Enable -Wwrite-strings warning flag"
             default "n"

tools/test_apps/system/build_test/sdkconfig.ci.no_merge_constants

@@ -0,0 +1 @@
+CONFIG_COMPILER_NO_MERGE_CONSTANTS=y