dmd ~master cannot compile vibe

Currently, the FE is set at 2066, but D-Programming-Language/phobos#1910 isn't pulled yet, so it breaks the compilation.
Also, there is another issue, which currently prevent me from using vibe.d master, but it's more likely to be a compiler bug:
````
Compiling source/vibe/core/task.d...
Writing to: .dub/build/libevent-debug-linux.posix-x86_64-/tmp/result/bin/dmd-B8D9EA0D4C1B9C5BD0A7181866C46640/source.vibe.core.task.d.o
/tmp/result/bin/dmd -c -of.dub/build/libevent-debug-linux.posix-x86_64-/tmp/result/bin/dmd-B8D9EA0D4C1B9C5BD0A7181866C46640/source.vibe.core.task.d.o -debug -g -w -version=VibeLibeventDriver -version=Have_vibe_d -version=Have_libevent -version=Have_openssl -Isource/ -I../../../../.dub/packages/libevent-master -I../../../../.dub/packages/openssl-master source/vibe/core/task.d
source/vibe/core/task.d(105): Error: expression newStdConcurrency of type newStdConcurrency does not have a boolean value
source/vibe/core/task.d(136): Error: expression newStdConcurrency of type newStdConcurrency does not have a boolean value
source/vibe/core/core.d(1120): Error: FixedRingBuffer!CoreTask had previous errors
source/vibe/core/task.d(31): Error: expression newStdConcurrency of type newStdConcurrency does not have a boolean value
source/vibe/core/task.d(71): Error: expression newStdConcurrency of type newStdConcurrency does not have a boolean value
source/vibe/core/drivers/libevent2.d(582): Error: ArraySet!Task had previous errors
source/vibe/core/drivers/libevent2.d(585): Error: template instance vibe.utils.hashmap.HashMap!(Thread, ThreadSlot, DefaultHashMapTraits!(Thread)) error instantiating
FAIL .dub/build/libevent-debug-linux.posix-x86_64-/tmp/result/bin/dmd-B8D9EA0D4C1B9C5BD0A7181866C46640/ vibe-d staticLibrary
Error executing command build: /tmp/result/bin/dmd failed with exit code 1
````

I get this with ~master, gdc & dmd with FE 2065, and dmd v2.064.X doesn't even compile with digger.
*NOTE*: This is a tainted dub with implements `--build-mode=singleFile`. However, I work on this because in the first place, my shell script that did the same work hit the same problem. This only happen in `singleFile` mode, not in `allAtOnce` or `separate`.