plugins/c_src.mk: use non-regex file extention detection

* The `-regex` option of `find` command to determine `SOURCES` in
  plugins/c_src.mk` is not portable; does not work on OS X.
  Rewrite with a portable form of using `find` native `-name`
  command option with `\(`, `-o`, and `\)`.

* Support file extentions of `*.c`, `*.C`, `*.cc`, and `*.cpp`.

erlang.mk

@@ -632,7 +632,7 @@ clean::
 	$(MAKE) -C $(C_SRC_DIR) clean
 
 else
-SOURCES := $(shell find $(C_SRC_DIR) -type f -regex ".*\.\(C\|cc?\|cpp\)")
+SOURCES := $(shell find $(C_SRC_DIR) -type f \( -name "*.c" -o -name "*.C" -o -name "*.cc" -o -name "*.cpp" \))
 OBJECTS = $(addsuffix .o, $(basename $(SOURCES)))
 
 COMPILE_C = $(c_verbose) $(CC) $(CFLAGS) $(CPPFLAGS) -c

plugins/c_src.mk

@@ -55,7 +55,7 @@ clean::
 	$(MAKE) -C $(C_SRC_DIR) clean
 
 else
-SOURCES := $(shell find $(C_SRC_DIR) -type f -regex ".*\.\(C\|cc?\|cpp\)")
+SOURCES := $(shell find $(C_SRC_DIR) -type f \( -name "*.c" -o -name "*.C" -o -name "*.cc" -o -name "*.cpp" \))
 OBJECTS = $(addsuffix .o, $(basename $(SOURCES)))
 
 COMPILE_C = $(c_verbose) $(CC) $(CFLAGS) $(CPPFLAGS) -c