Drop use of 'make avail' following https://github.com/cc65/cc65/pull/1994

cc65's 'make avail' now fails unless all targets were built.
Create links explicitly for ca65/ld65 only.

README.md

@@ -6,3 +6,24 @@ This action will build and install the cc65 assembler components (ca65, ld65).
 * Targets are built and installed, so later steps can use the `ca65` and `ld65` commands directly.
 
 The action has no inputs or outputs.
+
+## Example
+
+```yml
+name: build
+
+on:
+  push:
+    branches: [ main ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: a2stuff/build-install-ca65-action@v1
+      - name: build
+        run: |
+          ca65 -o example.o example.s
+          ld65 --config example.cfg -o example example.o
+```

action.yml

@@ -5,6 +5,8 @@ runs:
   steps:
     - run: >
         git clone https://github.com/cc65/cc65 /tmp/cc65 &&
-        sudo make -C /tmp/cc65 ca65 ld65 avail &&
+        sudo make -C /tmp/cc65 ca65 ld65 &&
+        sudo ln -s /tmp/cc65/bin/ca65 /usr/local/bin/ca65 &&
+        sudo ln -s /tmp/cc65/bin/ld65 /usr/local/bin/ld65 &&
         ca65 --version
       shell: bash