remove totally invalid gcc arguments from cross file

Partial revert of commit cf23e34187. This
mostly moved existing arguments to the "right" location, but also
introduced new arguments that didn't previously exist -- which was
wrong.

... also, these cross files are used by CI (if they have a corresponding
.json file) and this change broke the CI. Because --target isn't a valid
gcc option, although clang/rustc do accept it. For GCC, the argument
parser decides you wanted --target-help, which prints documentation text
and then quits.

cross/ubuntu-armhf.txt

@@ -1,8 +1,8 @@
 [binaries]
 # we could set exe_wrapper = qemu-arm-static but to test the case
 # when cross compiled binaries can't be run we don't do that
-c = ['/usr/bin/arm-linux-gnueabihf-gcc', '--target', 'arm-unknown-linux-gnueabihf']
-cpp = ['/usr/bin/arm-linux-gnueabihf-g++', '--target', 'arm-unknown-linux-gnueabihf']
+c = ['/usr/bin/arm-linux-gnueabihf-gcc']
+cpp = ['/usr/bin/arm-linux-gnueabihf-g++']
 rust = ['rustc', '--target', 'arm-unknown-linux-gnueabihf', '-C', 'linker=/usr/bin/arm-linux-gnueabihf-gcc-7']
 ar = '/usr/arm-linux-gnueabihf/bin/ar'
 strip = '/usr/arm-linux-gnueabihf/bin/strip'