Bump erlang.mk

by running
```
make erlang-mk
```

to include ninenines/erlang.mk@6423c1c
which provides test coverage for individual suites.

Author: ansd

erlang.mk

@@ -17,7 +17,7 @@
 ERLANG_MK_FILENAME := $(realpath $(lastword $(MAKEFILE_LIST)))
 export ERLANG_MK_FILENAME
 
-ERLANG_MK_VERSION = bf7a194
+ERLANG_MK_VERSION = 6423c1c
 ERLANG_MK_WITHOUT = 
 
 # Make 3.81 and 3.82 are deprecated.
@@ -6285,9 +6285,9 @@ ifeq ($(PLATFORM),msys2)
 	CXXFLAGS ?= -O3 -finline-functions -Wall
 else ifeq ($(PLATFORM),darwin)
 	CC ?= cc
-	CFLAGS ?= -O3 -std=c99 -arch x86_64 -Wall -Wmissing-prototypes
-	CXXFLAGS ?= -O3 -arch x86_64 -Wall
-	LDFLAGS ?= -arch x86_64 -flat_namespace -undefined suppress
+	CFLAGS ?= -O3 -std=c99 -Wall -Wmissing-prototypes
+	CXXFLAGS ?= -O3 -Wall
+	LDFLAGS ?= -flat_namespace -undefined suppress
 else ifeq ($(PLATFORM),freebsd)
 	CC ?= cc
 	CFLAGS ?= -O3 -std=c99 -finline-functions -Wall -Wmissing-prototypes
@@ -6707,9 +6707,9 @@ endif
 endif
 
 define ct_suite_target
-ct-$(1): test-build
-	$(verbose) mkdir -p $(CT_LOGS_DIR)
-	$(gen_verbose_esc) $(CT_RUN) -sname ct_$(PROJECT) -suite $(addsuffix _SUITE,$(1)) $(CT_EXTRA) $(CT_OPTS)
+ct-$1: test-build
+	$$(verbose) mkdir -p $$(CT_LOGS_DIR)
+	$$(gen_verbose_esc) $$(CT_RUN) -sname ct_$$(PROJECT) -suite $$(addsuffix _SUITE,$1) $$(CT_EXTRA) $$(CT_OPTS)
 endef
 
 $(foreach test,$(CT_SUITES),$(eval $(call ct_suite_target,$(test))))