toolchain: prepare to pass more additional CFLAGS via the wrapper

toolchain: prepare to pass more additional CFLAGS via the wrapper

Currently, we pass the user-supplied so-called target optimisation flags
to the wrapper.

We're going to have additional such CFLAGS to pass, so push-back the
formatting loop to quote the options at the last moment.

Reported-by: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: "Yann E. MORIN" <yann.morin@orange.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>