improve build cycle (avoid double evaluation if compiler specified as argument, e. g. like in GHA workflow step)

Author: sebres

CPP/build-lx.sh

@@ -31,19 +31,28 @@ function build() {
 
 export ARCH=$(arch)
 
-for c in gcc clang; do
+c="$@"
+if [ "$c" = "" ]; then
+  c="gcc clang"
+fi
+for c in $c; do
 
-  if   [ "$1" = "" ] || [ "$1" = "gcc" ]; then
-    # use gcc/g++
-    export CC="gcc"
-    export CXX="g++"
-    export OUTDIR="$PWD/build-gcc"
-  elif [ "$1" = "" ] || [ "$1" = "clang" ]; then
-    # use clang
-    export CC="clang"
-    export CXX="clang++"
-    export OUTDIR="$PWD/build-clang"
-  fi
+  echo "Build ($c) ..."
+  export CC="$c"
+  case "$c" in
+    gcc)
+      export CXX="g++"
+      export OUTDIR="$PWD/build-gcc"
+    ;;
+    clang)
+      export CXX="clang++"
+      export OUTDIR="$PWD/build-clang"
+    ;;
+    *)
+      echo "Unsupported compiler: $c"
+      exit 1
+      ;;
+  esac
 
   mkdir -p "$OUTDIR"