Remove SPC_NO_MUSL_PATH, remove --libc, use SPC_LIBC instead (#642)

* Remove SPC_NO_MUSL_PATH, remove --libc, use SPC_LIBC instead

* Fix tests

* Internally use GNU_ARCH for unified

* Update EXTENSION_DIR comments for env.ini

* Remove redundant -fPIC cflags in curl

.github/workflows/tests.yml

@@ -100,14 +100,13 @@ jobs:
           path: vendor
           key: ${{ runner.os }}-php-${{ hashFiles('**/composer.lock') }}
           restore-keys: |
-            ${{ runner.os }}-php-
+            ${{ runner.os }}-php
 
       - name: "Install Dependencies"
         run: composer install -q --no-ansi --no-interaction --no-scripts --no-progress --prefer-dist
 
       - name: "Run PHPUnit Tests"
-        run: |
-          SPC_NO_MUSL_PATH=yes vendor/bin/phpunit tests/ --no-coverage
+        run: SPC_LIBC=glibc vendor/bin/phpunit tests/ --no-coverage
 
   define-matrix:
     name: "Define Matrix"