scripts: Update GCC build script to build GCC 10.2

Change-Id: Ie0927e7afa03ecd64df6d3033819e118e9e1eec6

download-toolchain.sh

diff --git a/download-toolchain.sh b/download-toolchain.sh
index 01175f3..5a9974c 100755
--- a/download-toolchain.sh
+++ b/download-toolchain.sh
@@ -33,7 +33,7 @@
 TOOLCHAIN_SRC="${OUT}/tmp/toolchain"
 LLVM_SRC="${TOOLCHAIN_SRC}/llvm-project"
 
-TOOLCHAINLLVM_TAG="2021.06.26"
+TOOLCHAINLLVM_TAG="2021.06.18"
 TOOLCHAINLLVM_BINUTILS_BRANCH="rvv-1.0.x-zfh"