helper,rtos,server: Restore missing warning flags

These libraries override the used CFLAGS without adding the
defaults. This didn't have any effect until change
http://openocd.zylin.com/3870 (ef4c139). Restore by adding
AM_CLAGS to the per-target CFLAGS.

Interestingly, automake seems to clear the CFLAGS for the target
even if the override variable is only mentioned within a non-active
conditional branch, such as the IS_MINGW for the affected libraries.

Change-Id: I805206865e59e3fa33a7ea3c0d3472e51219351c
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/3927
Tested-by: jenkins
Reviewed-by: Paul Fertser <fercerpav@gmail.com>

src/helper/Makefile.am

@@ -37,7 +37,7 @@ else
 %C%_libhelper_la_SOURCES += %D%/ioutil_stubs.c
 endif
 
-%C%_libhelper_la_CFLAGS =
+%C%_libhelper_la_CFLAGS = $(AM_CFLAGS)
 if IS_MINGW
 # FD_* macros are sloppy with their signs on MinGW32 platform
 %C%_libhelper_la_CFLAGS += -Wno-sign-compare

src/rtos/Makefile.am

@@ -24,7 +24,7 @@ noinst_LTLIBRARIES += %D%/librtos.la
 	%D%/rtos_mqx_stackings.h \
 	%D%/rtos_ucos_iii_stackings.h
 
-%C%_librtos_la_CFLAGS =
+%C%_librtos_la_CFLAGS = $(AM_CFLAGS)
 
 if IS_MINGW
 # FD_* macros are sloppy with their signs on MinGW32 platform

src/server/Makefile.am

@@ -10,7 +10,7 @@ noinst_LTLIBRARIES += %D%/libserver.la
 	%D%/tcl_server.c \
 	%D%/tcl_server.h
 
-%C%_libserver_la_CFLAGS =
+%C%_libserver_la_CFLAGS = $(AM_CFLAGS)
 if IS_MINGW
 # FD_* macros are sloppy with their signs on MinGW32 platform
 %C%_libserver_la_CFLAGS += -Wno-sign-compare