build/toolchain/musl-host-gcc: handle non-workspace-root execution

This is needed to build stdlib with cgo, which is in turn required for
the race checker to be enabled.

Change-Id: Ic81542925a02c626f157dfd8c6650de3dbb30c7d
Reviewed-on: https://review.monogon.dev/c/monogon/+/1832
Tested-by: Jenkins CI
Reviewed-by: Leopold Schabel <leo@monogon.tech>
diff --git a/build/toolchain/musl-host-gcc/gcc-wrapper.sh b/build/toolchain/musl-host-gcc/gcc-wrapper.sh
index a430e75..33048c0 100755
--- a/build/toolchain/musl-host-gcc/gcc-wrapper.sh
+++ b/build/toolchain/musl-host-gcc/gcc-wrapper.sh
@@ -1,2 +1,3 @@
 #!/usr/bin/env bash
-exec /usr/bin/gcc "$@" -specs build/toolchain/musl-host-gcc/musl.spec
+SCRIPT_DIR=$( cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )
+exec /usr/bin/gcc "$@" -specs $SCRIPT_DIR/musl.spec