auto merge of #6836 : pnkfelix/rust/fsk-issue6805-ccache-rewrite-basedir, r=catamorphism

Attempt to get reuse of common object code from multiple clones in different directories.

This is a followup to issue #6805.

Author: bors

configure

@@ -970,6 +970,13 @@ then
     putvar CFG_CCACHE_CPP2
 fi
 
+if [ ! -z "$CFG_ENABLE_CCACHE" ]
+then
+    CFG_CCACHE_BASEDIR=${CFG_SRC_DIR}
+    putvar CFG_CCACHE_BASEDIR
+fi
+
+
 if [ ! -z $BAD_PANDOC ]
 then
     CFG_PANDOC=

mk/platform.mk

@@ -396,6 +396,11 @@ ifeq ($(CFG_CCACHE_CPP2),1)
   export CCACHE_CPP
 endif
 
+ifdef CFG_CCACHE_BASEDIR
+  CCACHE_BASEDIR=$(CFG_CCACHE_BASEDIR)
+  export CCACHE_BASEDIR
+endif
+
 define CFG_MAKE_TOOLCHAIN
   CFG_COMPILE_C_$(1) = $$(CC_$(1))  \
         $$(CFG_GCCISH_CFLAGS)      \