rules: Refactoring and minor improvements

Compared to the previous commit, the action graphs for just
and its unit tests are unchanged.
- Git hash of action graph for ["",""]:
    c6e75f17abd7ffaab6ff9bb725ad67ec0bf6c973
- Git hash of action graph for ["test/buildtool","TESTS"]:
    8063dfb3dd7daa9ae01d95c177e14946f785c57e

Refactor:
- "local cflags" to "private-cflags"
- "local defines" to "private-defines"
- "link externals" to "private-ldflags"
- "deps" to "private-deps" for (test) binaries
- "proto" to "private-proto" for binaries

Improvements:
- consistent variable declaration order:
    OS, ARCH, HOST_ARCH, TARGET_ARCH,
    CC, CXX, CFLAGS, CXXFLAGS, ADD_CFLAGS, ADD_CXXFLAGS,
    AR, ENV, PATH
- use fields close to their definition (in RULES)
- use common expression for binaries and test binaries
- split expression "flags" and "compiler"
  ... to separate ones for CC and CXX.
- rename "transition" to "deps-transition"
  ... to avoid conflicts with other transitions.
- support "defaults-transition" for CC expressions

Implement:
- "cflags" for libraries
- "private-cflags" for (test) binaries
- "private-defines" for test binaries
- "private-ldflags" for test binaries
- (public) "defines" for libraries

1 files changed, 4 insertions, 4 deletions

diff --git a/CC/auto/RULES b/CC/auto/RULES
index ab1e689..2429634 100644
--- a/CC/auto/RULES
+++ b/CC/auto/RULES
@@ -24,12 +24,12 @@
       ]
     }
   , "config_doc":
-    { "CXX":
-      [ "The name of the C++ compiler to be used by checks. If None, the"
+    { "CC":
+      [ "The name of the C compiler to be used by checks. If None, the"
       , "respective value from [\"CC\", \"defaults\"] will be taken."
       ]
-    , "CC":
-      [ "The name of the C compiler to be used by checks. If None, the"
+    , "CXX":
+      [ "The name of the C++ compiler to be used by checks. If None, the"
       , "respective value from [\"CC\", \"defaults\"] will be taken."
       ]
     , "CFLAGS":