serial: remove unneccesary exports

There variables are only used directly in the main Makefile.include or in
application makefiles. So there is no need to export the value.

Not exporting will also prevent evaluating them for no reason when 'term' is not
done.

Author: cladmi

makefiles/tools/serial.inc.mk

@@ -8,15 +8,13 @@ endif
 ifeq ($(PORT),)
   $(info Warning: no PORT set!)
 endif
-export PORT
-
 export BAUD ?= 115200
 
 RIOT_TERMINAL ?= pyterm
 ifeq ($(RIOT_TERMINAL),pyterm)
-    export TERMPROG  ?= $(RIOTTOOLS)/pyterm/pyterm
-    export TERMFLAGS ?= -p "$(PORT)" -b "$(BAUD)"
+    TERMPROG  ?= $(RIOTTOOLS)/pyterm/pyterm
+    TERMFLAGS ?= -p "$(PORT)" -b "$(BAUD)"
 else ifeq ($(RIOT_TERMINAL),picocom)
-    export TERMPROG  ?= picocom
-    export TERMFLAGS ?= --nolock --imap lfcrlf --echo --baud "$(BAUD)" "$(PORT)"
+    TERMPROG  ?= picocom
+    TERMFLAGS ?= --nolock --imap lfcrlf --echo --baud "$(BAUD)" "$(PORT)"
 endif

makefiles/vars.inc.mk

@@ -71,9 +71,9 @@ export GIT_CACHE_DIR         # path to git-cache cache directory
 export FLASHER               # The command to call on "make flash".
 export FFLAGS                # The parameters to supply to FLASHER.
 export FLASH_ADDR            # Define an offset to flash code into ROM memory.
-export TERMPROG              # The command to call on "make term".
-export TERMFLAGS             # Additional parameters to supply to TERMPROG.
-export PORT                  # The port to connect the TERMPROG to.
+# TERMPROG                   # The command to call on "make term".
+# TERMFLAGS                  # Additional parameters to supply to TERMPROG.
+# PORT                       # The port to connect the TERMPROG to.
 export ELFFILE               # The unstripped result of the compilation.
 export HEXFILE               # The stripped result of the compilation.
 export DEBUGGER              # The command to call on "make debug", usually a script starting the GDB front-end.