cccl: Provide '-' before the options instead of double slash.

cccl: Provide '-' before the options instead of double slash.

While compiling Open vSwitch with visual c++ in
a mingw environment, I have observed that "//" before
options does not work for all the compiler options of
MSVC. Using "-" on the other hand seems to work.

Also, echo the command line options passed to
the MSVC compiler.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>