Allow running the script on a non-FreeBSD system about cheribuild

[arichardson]

Mostly works now, but compiling still fails:

clang version 3.8.0 (https://github.com/CTSRD-CHERI/clang.git 473591c52d2160071616e8574dc80305abfdda52) (https://github.com/CTSRD-CHERI/llvm.git 388f6926b8f9bb0557c65b74badb8a34734f13dc)
Target: cheri-unknown-freebsd11
Thread model: posix
InstalledDir: /build/cheri-on-linux/sdk256/bin
 "/build/cheri-on-linux/sdk256/bin/clang-3.8" -cc1 -triple cheri-unknown-freebsd11 -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -main-file-name testprog.c -mrelocation-model static -mthread-model posix -mdisable-fp-elim -masm-verbose -mconstructor-aliases -target-abi n64 -mfloat-abi hard -v -dwarf-column-info -resource-dir /build/cheri-on-linux/sdk256/bin/../lib/clang/3.8.0 -isysroot /build/cheri-on-linux/sdk256/sysroot -fdebug-compilation-dir /staticdata/sources/ctsrd/my-cheri-stuff/testprog -ferror-limit 19 -fmessage-length 164 -fobjc-runtime=gnustep -fdiagnostics-show-option -fcolor-diagnostics -cheri-linker -o /tmp/testprog-cd7b07.o -x c ./testprog.c
clang -cc1 version 3.8.0 based upon LLVM 3.8.0svn default target cheri-unknown-freebsd
#include "..." search starts here:
#include <...> search starts here:
 /build/cheri-on-linux/sdk256/bin/../lib/clang/3.8.0/include
 /build/cheri-on-linux/sdk256/sysroot/usr/include
End of search list.
 "/build/cheri-on-linux/sdk256/bin/ld" --sysroot=/build/cheri-on-linux/sdk256/sysroot --eh-frame-hdr -dynamic-linker /libexec/ld-elf.so.1 --enable-new-dtags -o ./testprog.cheri /build/cheri-on-linux/sdk256/sysroot/usr/lib/crt1.o /build/cheri-on-linux/sdk256/sysroot/usr/lib/crti.o /build/cheri-on-linux/sdk256/sysroot/usr/lib/crtbegin.o -L/build/cheri-on-linux/sdk256/sysroot/usr/lib /tmp/testprog-cd7b07.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /build/cheri-on-linux/sdk256/sysroot/usr/lib/crtend.o /build/cheri-on-linux/sdk256/sysroot/usr/lib/crtn.o
/build/cheri-on-linux/sdk256/sysroot/usr/lib/libgcc_s.so: could not read symbols: File in wrong format
clang-3.8: error: linker command failed with exit code 1 (use -v to see invocation)

[arichardson]

remote-cheribuild.py can be used