libosip2: arc: Undefine __arc__ when building for ARC processors

libosip2 appears to have support for the "ARC standard" (Advanced
RISC Computing), which is unrelated to Synopsys DesignWare ARC
processors. The check for this involves verifying the existence of
the "__arc__" macro. Unfortunately, this macro is also present
as a predefined built-in for the ARC processors, resulting into
build failures.

[Peter: add short comment in .mk files as well]
Signed-off-by: Mischa Jonker <mjonker@synopsys.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/libeXosip2/libeXosip2.mk

@@ -12,6 +12,11 @@ LIBEXOSIP2_LICENSE_FILES = COPYING
 
 LIBEXOSIP2_DEPENDENCIES = host-pkgconf libosip2
 
+ifeq ($(BR2_arc),y)
+# toolchain __arc__ define conflicts with libeXosip2 source
+LIBEXOSIP2_CONF_ENV += CFLAGS="$(TARGET_CFLAGS) -U__arc__"
+endif
+
 ifeq ($(BR2_PACKAGE_OPENSSL),y)
 LIBEXOSIP2_DEPENDENCIES += openssl
 LIBEXOSIP2_CONF_OPT += --enable-openssl

package/libosip2/libosip2.mk

@@ -10,6 +10,11 @@ LIBOSIP2_INSTALL_STAGING = YES
 LIBOSIP2_LICENSE = LGPLv2.1+
 LIBOSIP2_LICENSE_FILES = COPYING
 
+ifeq ($(BR2_arc),y)
+# toolchain __arc__ define conflicts with libosip2 source
+LIBOSIP2_CONF_ENV += CFLAGS="$(TARGET_CFLAGS) -U__arc__"
+endif
+
 LIBOSIP2_CONF_OPT = \
 	--enable-mt=$(if $(BR2_TOOLCHAIN_HAS_THREADS),yes,no)