Mk/bsd.ccache.mk: Add CCACHE_ENABLED variable for ports' convenience

Some projects do some special handling when the ccache program is present.
This causes problems because ports framework has its own ccache settings
and mere presence of ccache program doesn't mean that ccache is enabled.
The new CCACHE_ENABLED variable can be used to tell projects if ccache
is really enabled.

PR:		266310
Approved by:	tcberner@ (as portmgr)

Mk/bsd.ccache.mk

@@ -11,6 +11,7 @@
 #                       default.
 #
 # Port use (users should not modify these):
+#  - CCACHE_ENABLED - tells the port if ccache is enabled.
 #  - CCACHE_BIN - path to the ccache binary.  Intended to be prefixed before CC.
 #  - CCACHE_WRAPPER_PATH - path to directory containing compiler symlinks back
 #                          to ccache.  For example, gcc5 -> ccache.  Intended
@@ -42,11 +43,18 @@ _CCACHEMKINCLUDED=	yes
 NO_CCACHE=	t
 .  endif
 
+.  if defined(WITH_CCACHE_BUILD)
+CCACHE_ENABLED= yes
+.  else
+CCACHE_ENABLED= no
+.  endif
+
 # HOME is always set to ${WRKDIR} now. Try to use /root/.ccache as default.
 .  if defined(WITH_CCACHE_BUILD) && !defined(CCACHE_DIR)
 .    if defined(USER) && ${USER} == root
 CCACHE_DIR=	/root/.ccache
 .    else
+CCACHE_ENABLED=	no
 NO_CCACHE=	yes
 WARNING+=	WITH_CCACHE_BUILD support disabled, please set CCACHE_DIR.
 .    endif