use env to set environment variables for GBE_BIN_GENERATER
use env to set environment variables for GBE_BIN_GENERATER

cmake interprets OCL_PCM_PATH=... as a command and will enclose it in
quotes in case it contains characters requiring protection, e.g. ~
a quoted "FOO=bar" is interpreted by /bin/sh as a command (that does not
exist), not a variable setting for a following command

use env to set the variables unambiguously

Signed-off-by: Andreas Beckmann <6a67b89c45772a3e34a2045a2631c0b9ed72f211@debian.org>
Reviewed-by: Zhigang Gong <e04a7b9b70b1e4c6318cf117dcd1a9056e14b97a@linux.intel.com>

freedesktop-unofficial-mirror/beignet,freedesktop-unofficial-mirror/beignet,wdv4758h/beignet,freedesktop-unofficial-mirror/beignet,wdv4758h/beignet,zhenyw/beignet,wdv4758h/beignet,wdv4758h/beignet,zhenyw/beignet,zhenyw/beignet,zhenyw/beignet,zhenyw/beignet,wdv4758h/beignet,freedesktop-unofficial-mirror/beignet