Revert "crossgcc: Upgrade GCC to 9.2.0"

Revert the upgrade as it breaks at least the devicetree parser on
aarch64, tested on qemu aarch64 target.

This reverts commit dfd3f21174.

Change-Id: I65607817188db21533014caa6d15be9a2004d498
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/39571
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/crossgcc/patches/gcc-8.3.0_gnat.patch

@@ -0,0 +1,11 @@
+--- gcc-6.1.0/gcc/ada/gcc-interface/Make-lang.in.bak	2015-08-24 16:23:25.004493665 +0200
++++ gcc-6.1.0/gcc/ada/gcc-interface/Make-lang.in	2015-08-24 17:53:52.496636113 +0200
+@@ -45,7 +45,7 @@
+ 
+ 
+ # Extra flags to pass to recursive makes.
+-COMMON_ADAFLAGS= -gnatpg
++COMMON_ADAFLAGS= -gnatpg -gnatwGUR
+ ifeq ($(TREECHECKING),)
+ CHECKING_ADAFLAGS=
+ else