Add a CHECK_XFAILS target that inverts the sense of check: it tries to compile and run the tests marked as XFAILs.

Author: graydon

src/Makefile

@@ -577,10 +577,18 @@ RFAIL_RS := $(wildcard test/run-fail/*.rs)
 CFAIL_RC := $(wildcard test/compile-fail/*.rc)
 CFAIL_RS := $(wildcard test/compile-fail/*.rs)
 
+ifdef CHECK_XFAILS
+TEST_RPASS_CRATES_X86 := $(filter $(TEST_XFAILS_X86), $(RPASS_RC))
+TEST_RPASS_CRATES_LLVM := $(filter $(TEST_XFAILS_LLVM), $(RPASS_RC))
+TEST_RPASS_SOURCES_X86 := $(filter $(TEST_XFAILS_X86), $(RPASS_RS))
+TEST_RPASS_SOURCES_LLVM := $(filter $(TEST_XFAILS_LLVM), $(RPASS_RS))
+else
 TEST_RPASS_CRATES_X86 := $(filter-out $(TEST_XFAILS_X86), $(RPASS_RC))
 TEST_RPASS_CRATES_LLVM := $(filter-out $(TEST_XFAILS_LLVM), $(RPASS_RC))
 TEST_RPASS_SOURCES_X86 := $(filter-out $(TEST_XFAILS_X86), $(RPASS_RS))
 TEST_RPASS_SOURCES_LLVM := $(filter-out $(TEST_XFAILS_LLVM), $(RPASS_RS))
+endif
+
 TEST_RPASS_EXTRAS := $(wildcard test/run-pass/*/*.rs)
 TEST_RPASS_EXES_X86 := \
                       $(TEST_RPASS_CRATES_X86:.rc=.x86$(CFG_EXE_SUFFIX)) \