Remove 'dangerous' instructions from the example make.conf.

Clarify when and why these might be used and that this isn't a supported
configuration.

PR:		docs/144488
Submitted by:	amdmi3
Approved by:	cperciva (implicit)
MFC after:	2 weeks

share/examples/etc/make.conf

@@ -57,21 +57,20 @@
 # CFLAGS controls the compiler settings used when compiling C code.
 # Note that optimization settings other than -O and -O2 are not recommended
 # or supported for compiling the world or the kernel - please revert any
-# nonstandard optimization settings to "-O" or "-O2 -fno-strict-aliasing"
+# nonstandard optimization settings
 # before submitting bug reports without patches to the developers.
 #
-# Compiling with -fstrict-aliasing optimization breaks some [notable] ports.
-# GCC turns on -fstrict-aliasing optimization at all levels above -O[1], so
-# explicitly turn it off when using compiling with the -O2 optimization level.
-#
-#CFLAGS= -O2 -fno-strict-aliasing -pipe
-#
 # CXXFLAGS controls the compiler settings used when compiling C++ code.
 # Note that CXXFLAGS is initially set to the value of CFLAGS.  If you wish
 # to add to CXXFLAGS value, "+=" must be used rather than "=".  Using "="
 # alone will remove the often needed contents of CFLAGS from CXXFLAGS.
 #
-#CXXFLAGS+= -fconserve-space
+# Additional compiler flags can be specified that extend or override
+# default ones. However, neither the base system nor ports are guaranteed
+# to build and function without problems with non-default settings.
+#
+# CFLAGS+=	-msse3
+# CXXFLAGS+=	-msse3
 #
 # MAKE_SHELL controls the shell used internally by make(1) to process the
 # command scripts in makefiles.  Three shells are supported, sh, ksh, and