Use core platform detection in c_src

plugins/c_src.mk

@@ -11,17 +11,16 @@ C_SRC_OUTPUT ?= $(CURDIR)/priv/$(PROJECT).so
 
 # System type and C compiler/flags.
 
-UNAME_SYS := $(shell uname -s)
-ifeq ($(UNAME_SYS), Darwin)
+ifeq ($(PLATFORM),darwin)
 	CC ?= cc
 	CFLAGS ?= -O3 -std=c99 -arch x86_64 -finline-functions -Wall -Wmissing-prototypes
 	CXXFLAGS ?= -O3 -arch x86_64 -finline-functions -Wall
 	LDFLAGS ?= -arch x86_64 -flat_namespace -undefined suppress
-else ifeq ($(UNAME_SYS), FreeBSD)
+else ifeq ($(PLATFORM),freebsd)
 	CC ?= cc
 	CFLAGS ?= -O3 -std=c99 -finline-functions -Wall -Wmissing-prototypes
 	CXXFLAGS ?= -O3 -finline-functions -Wall
-else ifeq ($(UNAME_SYS), Linux)
+else ifeq ($(PLATFORM),linux)
 	CC ?= gcc
 	CFLAGS ?= -O3 -std=c99 -finline-functions -Wall -Wmissing-prototypes
 	CXXFLAGS ?= -O3 -finline-functions -Wall