change(bootloader): rename bootloader.ld -> bootloader.ld.in

This change passes file through compiler preprocessor which unlocks
future code refactoring.

tools/cmake/linker_script_preprocessor.cmake

@@ -0,0 +1,15 @@
+# Split CFLAGS string into list for proper argument passing
+# Uses UNIX_COMMAND method because NATIVE_COMMAND has issues on Windows
+# where the first argument is parsed specially, causing problems with quoted paths
+# Note: Paths are expected to be quoted in the CFLAGS variable
+separate_arguments(CFLAGS_LIST UNIX_COMMAND "${CFLAGS}")
+
+execute_process(COMMAND "${CC}" "-C" "-P" "-x" "c" "-E" ${CFLAGS_LIST} "${SOURCE}"
+                RESULT_VARIABLE RET_CODE
+                OUTPUT_VARIABLE PREPROCESSED_LINKER_SCRIPT
+                ERROR_VARIABLE ERROR_VAR)
+if(RET_CODE AND NOT RET_CODE EQUAL 0)
+    message(FATAL_ERROR "Can't generate ${TARGET}\nRET_CODE: ${RET_CODE}\nERROR_MESSAGE: ${ERROR_VAR}")
+endif()
+string(REPLACE "\\n" "\n" TEXT "${PREPROCESSED_LINKER_SCRIPT}")
+file(WRITE "${TARGET}" "${TEXT}")