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

2 files changed, 4 insertions, 4 deletions

diff --git a/src/buildtool/main/TARGETS b/src/buildtool/main/TARGETS
index 079d3f40..36a8cbff 100644
--- a/src/buildtool/main/TARGETS
+++ b/src/buildtool/main/TARGETS
@@ -3,7 +3,7 @@
   , "arguments_config": ["BUILD_STATIC_BINARY"]
   , "name": ["just"]
   , "srcs": ["main.cpp"]
-  , "deps":
+  , "private-deps":
     [ ["src/buildtool/common", "cli"]
     , ["src/buildtool/common", "config"]
     , ["src/buildtool/compatibility", "compatibility"]
@@ -23,7 +23,7 @@
     , "describe"
     ]
   , "stage": ["src", "buildtool", "main"]
-  , "link external":
+  , "private-ldflags":
     { "type": "if"
     , "cond": {"type": "var", "name": "BUILD_STATIC_BINARY"}
     , "then": ["-static"]
@@ -101,7 +101,7 @@
   , "name": ["version"]
   , "hdrs": ["version.hpp"]
   , "srcs": ["version.cpp"]
-  , "local defines":
+  , "private-defines":
     { "type": "++"
     , "$1":
       [ { "type": "if"
diff --git a/src/buildtool/system/TARGETS b/src/buildtool/system/TARGETS
index ddc7ae4d..11c2bd47 100644
--- a/src/buildtool/system/TARGETS
+++ b/src/buildtool/system/TARGETS
@@ -4,7 +4,7 @@
   , "name": ["system"]
   , "hdrs": ["system.hpp"]
   , "srcs": ["system.cpp"]
-  , "local defines":
+  , "private-defines":
     { "type": "if"
     , "cond": {"type": "var", "name": "VALGRIND_BUILD"}
     , "then": ["VALGRIND_BUILD"]