esp32/esp32_common.cmake: Allow overriding linker.lf.

Particularly for out of tree builds, one may need to provide alternative or
extra linker fragment files, or specify an absolute path to the default
`linker.lf` file.

In the default case, do nothing, provide a plain `linker.lf`, as before.

Signed-off-by: Karl Palsson <karl.palsson@marel.com>

ports/esp32/esp32_common.cmake

@@ -178,6 +178,13 @@ list(APPEND IDF_COMPONENTS
     vfs
 )
 
+# Provide the default LD fragment if not set
+if (MICROPY_USER_LDFRAGMENTS)
+    set(MICROPY_LDFRAGMENTS ${MICROPY_USER_LDFRAGMENTS})
+else()
+    set(MICROPY_LDFRAGMENTS linker.lf)
+endif()
+
 # Register the main IDF component.
 idf_component_register(
     SRCS
@@ -197,7 +204,7 @@ idf_component_register(
         ${MICROPY_BOARD_DIR}
         ${CMAKE_BINARY_DIR}
     LDFRAGMENTS
-        linker.lf
+        ${MICROPY_LDFRAGMENTS}
     REQUIRES
         ${IDF_COMPONENTS}
 )