Removed hardcoded `-arch x86_64` for MacOS nifs

For current macs the flag seems problematic as it overrides
the default choice of building for the current architecture
and hence prevents building on ARM based macs.

plugins/c_src.mk

@@ -35,9 +35,9 @@ 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