docker: fix gcc symlinks when base image has newer gcc

The unversioned symlinks was not created when the base image
already had a gcc installed (e.g. gcc-14 on Debian Trixie),
which made gcc-13 image use wrong compiler version.

Also skip the symlink step completely for clang images since
they don't need it.

Signed-off-by: Anders Roxell <anders.roxell@linaro.org>

Author: roxell

support/docker/Dockerfile.build

@@ -198,12 +198,12 @@ RUN set -x; \
 
 # For gcc images, symlink all binaries with unversioned names into $PATH
 ARG TOOLCHAIN_VERSION
-RUN for bin in $(ls -1 /usr/bin/*-${TOOLCHAIN_VERSION} | xargs -n 1 basename); do \
-    unver=${bin%-[0-9]*}; \
-    if [ ! -x /usr/bin/${unver} ]; then \
+RUN if [ -x /usr/bin/gcc-${TOOLCHAIN_VERSION} ]; then \
+    for bin in $(ls -1 /usr/bin/*-${TOOLCHAIN_VERSION} | xargs -n 1 basename); do \
+        unver=${bin%-[0-9]*}; \
         ln -sfv /usr/bin/$bin /usr/local/bin/${unver}; \
-        fi; \
-    done
+    done; \
+    fi
 
 # For clang images, symlink all the binaries in $PATH
 RUN if [ -d /usr/lib/llvm-*/bin ]; then ln -sfv /usr/lib/llvm-*/bin/* /usr/local/bin/; fi