Check compilation with USE_RVARGC on Github Actions

Co-authored-by: peterzhu2118 <peter@peterzhu.ca>

.github/workflows/compilers.yml

@@ -123,6 +123,7 @@ jobs:
 #         - { key: cppflags, name: USE_GC_MALLOC_OBJ_INFO_DETAILS, value: '-DUSE_GC_MALLOC_OBJ_INFO_DETAILS' }
           - { key: cppflags, name: USE_LAZY_LOAD,                  value: '-DUSE_LAZY_LOAD' }
 #         - { key: cppflags, name: USE_RINCGC=0,                   value: '-DUSE_RINCGC=0' }
+          - { key: cppflags, name: USE_RVARGC=1,                   value: '-DUSE_RVARGC=1' }
 #         - { key: cppflags, name: USE_SYMBOL_GC=0,                value: '-DUSE_SYMBOL_GC=0' }
 #         - { key: cppflags, name: USE_THREAD_CACHE=0,             value: '-DUSE_THREAD_CACHE=0' }
 #         - { key: cppflags, name: USE_TRANSIENT_HEAP=0,           value: '-DUSE_TRANSIENT_HEAP=0' }