BUILD: makefile: change default value of CC from gcc to cc

Change the default value of CC from gcc to cc to be more appropriate
for modern day mix of compilers. On GCC based OS's cc -> gcc. On Clang
based OS's cc -> clang. FreeBSD / OpenBSD have switched to Clang and
this corrects building with the proper compiler on OS's using Clang
as the default compiler. This especially matters for the necessity for
TLS on OpenBSD. I would expect this affects OpenMandriva and other
Linux OS's using Clang as well.
diff --git a/Makefile b/Makefile
index c064509..934ca16 100644
--- a/Makefile
+++ b/Makefile
@@ -58,8 +58,8 @@
 # given TARGET is enumerated at the end of "make help".
 #
 # Variables useful for packagers :
-#   CC is set to "gcc" by default and is used for compilation only.
-#   LD is set to "gcc" by default and is used for linking only.
+#   CC is set to "cc" by default and is used for compilation only.
+#   LD is set to "cc" by default and is used for linking only.
 #   ARCH may be useful to force build of 32-bit binary on 64-bit systems
 #   CFLAGS is automatically set for the specified CPU and may be overridden.
 #   LDFLAGS is automatically set to -g and may be overridden.
@@ -158,8 +158,7 @@
 ARCH =
 
 #### Toolchain options.
-# GCC is normally used both for compiling and linking.
-CC = gcc
+CC = cc
 LD = $(CC)
 
 #### Debug flags (typically "-g").