rdmd_test do not pass on Mac OSX

[Geod24]

Transferred from: https://issues.dlang.org/show_bug.cgi?id=18402

Reported by @timotheecour (2018-02-08 21:21:34 CET), confirmed by me.
Timothee's report was:

rdmd: make -f posix.mak -j8 test => core.exception.AssertError@rdmd_test.d(373): Assertion failure

Tested today with -j8.

% make -f posix.mak test
for file in ascii iteration ; do \
		generated/osx/64/tests_extractor -i "./test/tests_extractor/${file}.d" | diff -p - "./test/tests_extractor/${file}.d.ext"; \
	done
parsing test/tests_extractor/ascii.d
parsing test/tests_extractor/iteration.d
generated/osx/64/tests_extractor -a betterc -i "./test/tests_extractor/attributes.d" | diff -p - "./test/tests_extractor/attributes.d.ext";
parsing test/tests_extractor/attributes.d
generated/osx/64/tests_extractor --betterC -i "./test/tests_extractor/betterc.d" | diff -p - "./test/tests_extractor/betterc.d.ext";
parsing test/tests_extractor/betterc.d
generated/osx/64/rdmd_test generated/osx/64/rdmd -m64 \
	   --rdmd-default-compiler=../dmd/generated/osx/release/64/dmd \
	   --test-compilers=../dmd/generated/osx/release/64/dmd \

object.Exception@rdmd_test.d(696): /var/folders/1_/wzk0c3d17t37j8r1q8_3zl840000gn/T/dmd would not have been executed
----------------
??:? pure @safe void std.exception.bailOut!(Exception).bailOut(immutable(char)[], ulong, scope const(char)[]) [0x105fa83be]
??:? pure @safe bool std.exception.enforce!().enforce!(bool).enforce(bool, lazy const(char)[], immutable(char)[], ulong) [0x105faa7d4]
??:? void rdmd_test.runFallbackTest(immutable(char)[], immutable(char)[], immutable(char)[]) [0x105fa80fe]
??:? void rdmd_test.runCompilerAgnosticTests(immutable(char)[], immutable(char)[], immutable(char)[]) [0x105fa1146]
??:? _Dmain [0x105fa06fa]
make: *** [test_rdmd] Error 1

% dmd | head -n 1
DMD64 D Compiler v2.091.0
% git show HEAD
[...]
a1da2705dcffb4955f8065aee01a08602ad8216a

Tested on Mac OSX Catalina.