kamailio-5.x: fix build for new MIPS 4kec target

kamailio-5.x: fix build for new MIPS 4kec target

Recently support for target rtl838x was added to OpenWrt. It uses 4kec,
which is MIPS32. The Kamailio build system doesn't detect this and
treats it as MIPS I, adding -march=r3000 to the flags, which clashes
with -mips32r2.

mips-openwrt-linux-musl-gcc -mfp32 -march=r3000 -ftree-vectorize -fno-strict-overflow -pthread -DKSR_PTHREAD_MUTEX_SHARED -Wall -Os -pipe -mno-branch-likely -mips32r2 -mtune=4kec -fno-caller-saves -fno-plt -fhonour-copts -Wno-error=unused-but-set-variable -Wno-error=unused-result -msoft-float -I/builder/shared-workdir/build/sdk/staging_dir/target-mips_4kec_musl/usr/lib/libiconv-stub/include -I/builder/shared-workdir/build/sdk/staging_dir/target-mips_4kec_musl/usr/lib/libintl-stub/include -ffile-prefix-map=/builder/shared-workdir/build/sdk/build_dir/target-mips_4kec_musl/kamailio5-5.4.0=kamailio5-5.4.0 -Wformat -Werror=format-security -fstack-protector -D_FORTIFY_SOURCE=1 -Wl,-z,now -Wl,-z,relro -DVERSION_NODATE=1 -I/builder/shared-workdir/build/sdk/staging_dir/target-mips_4kec_musl/usr/include -I/builder/shared-workdir/build/sdk/staging_dir/toolchain-mips_4kec_gcc-8.4.0_musl/usr/include -I/builder/shared-workdir/build/sdk/staging_dir/toolchain-mips_4kec_gcc-8.4.0_musl/include/fortify -I/builder/shared-workdir/build/sdk/staging_dir/toolchain-mips_4kec_gcc-8.4.0_musl/include -I/builder/shared-workdir/build/sdk/staging_dir/target-mips_4kec_musl/usr/lib/libiconv-stub/include -I/builder/shared-workdir/build/sdk/staging_dir/target-mips_4kec_musl/usr/lib/libintl-stub/include   -DNAME='"kamailio"' -DVERSION='"5.4.0"' -DARCH='"mips"' -DOS='linux_' -DOS_QUOTED='"linux"' -DCOMPILER='"mips-openwrt-linux-musl-gcc 8.4.0"' -D__CPU_mips -D__OS_linux -DVERSIONVAL=5004000 -DCFG_DIR='"/etc/kamailio"' -DSHARE_DIR='"/usr/share/kamailio/"' -DRUN_DIR='"/var/run/kamailio/"' -DPKG_MALLOC -DSHM_MMAP -DDNS_IP_HACK -DUSE_MCAST -DUSE_TCP -DDISABLE_NAGLE -DHAVE_RESOLV_RES -DUSE_DNS_CACHE -DUSE_DNS_FAILOVER -DUSE_DST_BLACKLIST -DUSE_NAPTR -DWITH_XAVP -DMEM_JOIN_FREE -DF_MALLOC -DQ_MALLOC -DTLSF_MALLOC -DDBG_SR_MEMORY -DUSE_TLS -DTLS_HOOKS -DUSE_CORE_STATS -DSTATISTICS -DMALLOC_STATS -DUSE_SCTP -DMIPS_HAS_LLSC -DNOSMP -DCC_GCC_LIKE_ASM -DHAVE_GETHOSTBYNAME2 -DHAVE_UNION_SEMUN -DHAVE_SCHED_YIELD -DHAVE_MSG_NOSIGNAL -DHAVE_MSGHDR_MSG_CONTROL -DHAVE_ALLOCA_H -DHAVE_TIMEGM -DHAVE_SCHED_SETSCHEDULER -DHAVE_IP_MREQN -DUSE_RAW_SOCKS -DUSE_PTHREAD_MUTEX -DHAVE_EPOLL -DHAVE_SIGIO_RT -DSIGINFO64_WORKARROUND -DUSE_FUTEX -DHAVE_SELECT  -DMODS_DIR='"/usr/lib/kamailio/modules"' -c main.c -o main.o -MMD -MP
cc1: error: '-mips32r2' conflicts with the other architecture options, which specify a mips1 processor
Assembler messages:
Error: -mips32r2 conflicts with the other architecture options, which imply -mips1
Makefile.rules:100: recipe for target 'main.o' failed
make[5]: *** [main.o] Error 1

This commit fixes this by forcing ARCH to mips2 for 4kec CPUs as well
(Kamailio only differentiates between mips, mips2 and mips64).

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>