Clean up Makefile, move -Wredundant-decls to test build

CC always exists inside make so ?= doesn't assign to it

test/targets/gcc_auto_sizeof.yml

@@ -1,48 +0,0 @@
-compiler:
-  path: gcc
-  source_path:     '../src/'
-  unit_tests_path: &unit_tests_path 'tests/'
-  build_path:      &build_path 'build/'
-  options:
-    - '-c'
-    - '-m64'
-    - '-Wall'
-    - '-Wno-address'
-    - '-std=c99'
-    - '-pedantic'
-  includes:
-    prefix: '-I'
-    items:
-      - 'src/'
-      - '../src/'
-      - 'testdata/'
-      - *unit_tests_path
-  defines:
-    prefix: '-D'
-    items:
-      - UNITY_EXCLUDE_STDINT_H
-      - UNITY_EXCLUDE_LIMITS_H
-      - UNITY_INCLUDE_DOUBLE
-      - UNITY_SUPPORT_TEST_CASES
-      - UNITY_SUPPORT_64
-  object_files:
-    prefix: '-o'
-    extension: '.o'
-    destination: *build_path
-linker:
-  path: gcc
-  options:
-    - -lm
-    - '-m64'
-  includes:
-    prefix: '-I'
-  object_files:
-    path: *build_path
-    extension: '.o'
-  bin_files:
-    prefix: '-o'
-    extension: '.exe'
-    destination: *build_path
-colour: true
-:unity:
-  :plugins: []