pass IDF_TARGET variable to bootloader build process

components/bootloader/project_include.cmake

@@ -51,7 +51,7 @@ if((NOT CONFIG_SECURE_BOOT_ENABLED) OR
         # TODO: support overriding the bootloader in COMPONENT_PATHS
         SOURCE_DIR "${IDF_PATH}/components/bootloader/subproject"
         BINARY_DIR "${BOOTLOADER_BUILD_DIR}"
-        CMAKE_ARGS  -DSDKCONFIG=${SDKCONFIG} -DIDF_PATH=${IDF_PATH}
+        CMAKE_ARGS  -DSDKCONFIG=${SDKCONFIG} -DIDF_PATH=${IDF_PATH} -DIDF_TARGET=${IDF_TARGET}
                     -DSECURE_BOOT_SIGNING_KEY=${secure_boot_signing_key}
         INSTALL_COMMAND ""
         BUILD_ALWAYS 1  # no easy way around this...

components/bootloader/subproject/CMakeLists.txt

@@ -10,6 +10,11 @@ if(NOT IDF_PATH)
         "in by the parent build process.")
 endif()
 
+if(NOT IDF_TARGET)
+    message(FATAL_ERROR "Bootloader subproject expects the IDF_TARGET variable to be passed "
+        "in by the parent build process.")
+endif()
+
 set(COMPONENTS bootloader esptool_py partition_table soc bootloader_support log spi_flash micro-ecc main efuse)
 set(BOOTLOADER_BUILD 1)
 add_definitions(-DBOOTLOADER_BUILD=1)