Remove set -x from gcc wrappers

These are used very far down in the toolchain, where output is
unexpected and often noisy due to how often these tools are invoked.
Avoid printing unnecessary info.

Author: jyn514

docker/freebsd-gcc.sh

@@ -3,7 +3,6 @@
 # the freebsd images need libstdc++ to be linked as well
 # otherwise, we get `undefined reference to `std::ios_base::Init::Init()'`
 
-set -x
 set -euo pipefail
 
 main() {

docker/musl-gcc.sh

@@ -19,7 +19,6 @@
 #   missing soft-fp routine `__trunctfsf2`
 #   https://github.com/rust-lang/compiler-builtins/pull/483
 
-set -x
 set -euo pipefail
 
 main() {