feat(cmakev2/build): add __init_build() stub

Most of the global settings are configured in idf.cmake, but certain
elements can only be initialized after the project() function is called
and the toolchain is set up. For example, this includes the compilation
options, which may depend on identified compiler or the project name and
version set in the project() call. The __init_build function is called
at the beginning of the idf_build_library() function, meaning it should
be executed after the project() call. It ensures that initialization
occurs only once by setting the __BUILD_INITIALIZED build property.

Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>

tools/cmakev2/build.cmake

@@ -89,6 +89,24 @@ function(__dump_build_properties)
     endforeach()
 endfunction()
 
+#[[
+   __init_build()
+
+   Initialize settings that need to be configured after the project() function
+   is called. This primarily involves setting compilation options, define
+   settings, and configuring linker options.
+#]]
+function(__init_build)
+    idf_build_get_property(build_initialized __BUILD_INITIALIZED)
+    if(build_initialized)
+        # Ensure this function is executed only once throughout the entire
+        # project.
+        return()
+    endif()
+
+    idf_build_set_property(__BUILD_INITIALIZED YES)
+endfunction()
+
 #[[
    __get_library_interface_or_die(LIBRARY <library>
                                   OUTPUT <variable>)
@@ -243,6 +261,10 @@ function(idf_build_library)
         set(ARG_COMPONENTS "${component_names}")
     endif()
 
+    # Initialize settings that must be configured after the project() function
+    # is called.
+    __init_build()
+
     add_library("${ARG_INTERFACE}" INTERFACE)
     idf_build_set_property(LIBRARY_INTERFACES "${ARG_INTERFACE}" APPEND)
     idf_library_set_property("${ARG_INTERFACE}" LIBRARY_COMPONENTS "${ARG_COMPONENTS}")