Build system: Fix error if librtc submodule not available to bootloader

Closes #220 https://github.com/espressif/esp-idf/issues/220

components/bootloader/src/main/Makefile.projbuild

@@ -0,0 +1,4 @@
+# Submodules normally added in component.mk, but fully qualified
+# paths can be added at this level (we need binary librtc to be
+# available to link bootloader).
+COMPONENT_SUBMODULES += $(IDF_PATH)/components/esp32/lib

components/bootloader/src/main/component.mk

@@ -14,10 +14,10 @@ COMPONENT_ADD_LDFLAGS := -L $(COMPONENT_PATH) -lmain $(addprefix -T ,$(LINKER_SC
 
 COMPONENT_ADD_LINKER_DEPS := $(LINKER_SCRIPTS)
 
-ifdef IS_BOOTLOADER_BUILD
 # following lines are a workaround to link librtc into the
 # bootloader, until clock setting code is in a source-based esp-idf
 # component. See also rtc_printf() in bootloader_start.c
+#
+# See also matching COMPONENT_SUBMODULES line in Makefile.projbuild
 COMPONENT_ADD_LDFLAGS += -L $(IDF_PATH)/components/esp32/lib/ -lrtc_clk -lrtc
 COMPONENT_EXTRA_INCLUDES += $(IDF_PATH)/components/esp32/
-endif