Consolidate RUN for gcc install with other RUN

Author: Bronek

docker/debian/Dockerfile

@@ -158,20 +158,14 @@ FROM base AS clang
 # This is not inherited from base image, ensure no manual interaction needed.
 ARG DEBIAN_FRONTEND=noninteractive
 
-# Some build dependencies require GCC to be also available.
-RUN <<EOF
-apt-get update
-apt-get install -y --no-install-recommends gcc g++
-apt-get clean
-rm -rf /var/lib/apt/lists/*
-EOF
-
 # Install Clang. Use the LLVM apt repository to access the latest versions. We
 # must repeat the DEBIAN_VERSION argument here, as it is not inherited from the
-# base or source images.
+# base or source images. Some build dependencies require GCC to be also available.
 ARG DEBIAN_VERSION
 ARG CLANG_VERSION
 RUN <<EOF
+apt-get update
+apt-get install -y --no-install-recommends gcc g++
 curl --no-progress-meter https://apt.llvm.org/llvm-snapshot.gpg.key | gpg --dearmor -o /etc/apt/keyrings/llvm.gpg
 printf "%s\n%s\n" \
   "deb [signed-by=/etc/apt/keyrings/llvm.gpg] https://apt.llvm.org/${DEBIAN_VERSION}/ llvm-toolchain-${DEBIAN_VERSION}-${CLANG_VERSION} main" \

docker/ubuntu/Dockerfile

@@ -143,21 +143,15 @@ FROM base AS clang
 # This is not inherited from base image, ensure no manual interaction needed.
 ARG DEBIAN_FRONTEND=noninteractive
 
-# Some build dependencies require GCC to be also available.
-RUN <<EOF
-apt-get update
-apt-get install -y --no-install-recommends gcc g++
-apt-get clean
-rm -rf /var/lib/apt/lists/*
-EOF
-
-# Install Clang.
+# Install Clang. Some build dependencies require GCC to be also available.
 ARG CLANG_VERSION
 RUN <<EOF
 apt-get update
 apt-get install -y --no-install-recommends \
   clang-${CLANG_VERSION} \
-  llvm-${CLANG_VERSION}
+  llvm-${CLANG_VERSION} \
+  gcc \
+  g++
 apt-get clean
 rm -rf /var/lib/apt/lists/*
 update-alternatives \