samples: Support custom path to konanc in build.sh

samples/libcurl/build.sh

@@ -1,7 +1,12 @@
 #!/usr/bin/env bash
 
 DIR=$(cd "$(dirname "${BASH_SOURCE[0]}" )" && pwd )
-PATH=$DIR/../../dist/bin:$DIR/../../bin:$PATH
+
+if [ -z "$KONAN_HOME" ]; then
+    PATH="$DIR/../../dist/bin:$DIR/../../bin:$PATH"
+else
+    PATH="$KONAN_HOME/bin:$PATH"
+fi
 
 CFLAGS_macbook=-I/opt/local/include
 CFLAGS_linux="-I /usr/include -I /usr/include/x86_64-linux-gnu"