[time-sync] fix time sync and typo (#3637)

* fix typo in common-switches
* fix segment fault with time sync enabled

examples/Makefile-posix

@@ -60,6 +60,7 @@ SNTP_CLIENT                    ?= 1
 UDP_FORWARD                    ?= 1
 
 COMMONCFLAGS                   := \
+    -g                            \
     $(NULL)
 
 # If the user has asserted COVERAGE, alter the configuration options
@@ -80,7 +81,6 @@ configure_OPTIONS               = \
 ifneq ($(DEBUG),1)
 COMMONCFLAGS                   += \
     -O2                           \
-    -g                            \
     $(NULL)
 endif
 

examples/common-switches.mk

@@ -169,7 +169,7 @@ configure_OPTIONS              += --enable-sntp-client
 endif
 
 ifeq ($(TIME_SYNC),1)
-COMMONCFLAGS                   += -DPENTHREAD_CONFIG_ENABLE_TIME_SYNC=1
+COMMONCFLAGS                   += -DOPENTHREAD_CONFIG_ENABLE_TIME_SYNC=1 -DOPENTHREAD_CONFIG_HEADER_IE_SUPPORT=1
 endif
 
 ifeq ($(UDP_FORWARD),1)