configure: add missing cross compiler fallbacks

The arm compiler can be used for armeb, and the sparc64 compiler
can be used for sparc.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220517092616.1272238-9-pbonzini@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20220527153603.887929-20-alex.bennee@linaro.org>

configure

@@ -1827,6 +1827,7 @@ fi
 : ${cross_cc_cflags_aarch64_be="-mbig-endian"}
 : ${cross_cc_alpha="alpha-linux-gnu-gcc"}
 : ${cross_cc_arm="arm-linux-gnueabihf-gcc"}
+: ${cross_cc_armeb="$cross_cc_arm"}
 : ${cross_cc_cflags_armeb="-mbig-endian"}
 : ${cross_cc_hexagon="hexagon-unknown-linux-musl-clang"}
 : ${cross_cc_cflags_hexagon="-mv67 -O2 -static"}
@@ -1849,9 +1850,10 @@ fi
 : ${cross_cc_riscv64="riscv64-linux-gnu-gcc"}
 : ${cross_cc_s390x="s390x-linux-gnu-gcc"}
 : ${cross_cc_sh4="sh4-linux-gnu-gcc"}
-: ${cross_cc_cflags_sparc="-m32 -mcpu=supersparc"}
 : ${cross_cc_sparc64="sparc64-linux-gnu-gcc"}
 : ${cross_cc_cflags_sparc64="-m64 -mcpu=ultrasparc"}
+: ${cross_cc_sparc="$cross_cc_sparc64"}
+: ${cross_cc_cflags_sparc="-m32 -mcpu=supersparc"}
 : ${cross_cc_x86_64="x86_64-linux-gnu-gcc"}
 : ${cross_cc_cflags_x86_64="-m64"}