profiles: introduce XBPS_{,TARGET_}{ENDIAN,LIBC}

Provide new environment variables for simplifaction of template checks:
...ENDIAN defines the (target) machine's endianness: "le" or "be".
...LIBC defines the (target) machine's C library: "glibc" or "musl".

Closes: #13356
Signed-off-by: Jürgen Buchmüller <pullmoll@t-online.de>

common/build-profiles/i686.sh

@@ -1,3 +1,5 @@
+XBPS_ENDIAN=le
+XBPS_LIBC=glibc
 XBPS_WORDSIZE=32
 XBPS_TARGET_CFLAGS="-mtune=i686"
 XBPS_TARGET_CXXFLAGS="$XBPS_TARGET_CFLAGS"