toolchain/toolchain-external/toolchain-external-bootlin: flag OpenMP support

The fragments provided by toolchains.bootlin.com were incorrectly
flagging toolchains as not having OpenMP support while they had it
[0]. This has been fixed in toolchains.bootlin.com, so a run of
gen-bootlin-toolchains has allowed to adjust the toolchain definitions
in Buildroot, leading to this commit.

OpenMP support needs to be flagged so the proper libraries get copied
into the resultant filesystem to avoid missing dependencies [1].

[0]: https://github.com/bootlin/toolchains-builder/issues/60
[1]: https://bugs.busybox.net/show_bug.cgi?id=15634

Signed-off-by: Vincent Fazio <vfazio@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>