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, 1 insertions, 1 deletions

diff --git a/doc/tutorial/third-party-software.org b/doc/tutorial/third-party-software.org
index 7bce1c48..6fdde256 100644
--- a/doc/tutorial/third-party-software.org
+++ b/doc/tutorial/third-party-software.org
@@ -456,7 +456,7 @@ ambient system.
   , "name": ["fmt"]
   , "stage": ["fmt"]
   , "hdrs": [["TREE", null, "."]]
-  , "link external": ["-lfmt"]
+  , "private-ldflags": ["-lfmt"]
   }
 }
 #+END_SRC