Honour CC/AR/CFLAGS/CXXFLAGS/LDFLAGS in the luamake gcc backend and stop
it from stripping the binary at link time (Portage strips and splits debug
info itself).

--- a/3rd/luamake/scripts/compiler/gcc.lua
+++ b/3rd/luamake/scripts/compiler/gcc.lua
@@ -25,8 +25,10 @@
         ldflags[#ldflags+1] = "-lstdc++"
         ldflags[#ldflags+1] = "-Wl,-Bdynamic"
     end
-    if attribute.mode ~= "debug" then
-        ldflags[#ldflags+1] = "-s"
+    -- bentoo: never strip here, Portage does it (and splits debug info);
+    -- honour LDFLAGS from the environment instead.
+    for flag in (os.getenv "LDFLAGS" or ""):gmatch "%S+" do
+        ldflags[#ldflags+1] = flag
     end
     if attribute.lto ~= "off" then
         ldflags[#ldflags+1] = "-flto"
--- a/3rd/luamake/scripts/compiler/gcc_opt.lua
+++ b/3rd/luamake/scripts/compiler/gcc_opt.lua
@@ -1,6 +1,13 @@
 local globals = require "globals"
 local log = require "log"
 
+-- bentoo: append the distribution's compiler flags from the environment.
+-- They go last on the command line so that they win over upstream's
+-- defaults (-O2 and friends).
+local function env_flags(name)
+    return os.getenv(name) or ""
+end
+
 local function format_path(path)
     if path:match " " then
         return '"'..path..'"'
@@ -112,8 +119,8 @@
 end
 
 function gcc.rule_c(w, name, flags, cflags)
-    w:rule("c_"..name, ([[$cc -MMD -MT $out -MF $out.d %s %s -o $out -c $in]])
-        :format(cflags, flags),
+    w:rule("c_"..name, ([[$cc -MMD -MT $out -MF $out.d %s %s %s -o $out -c $in]])
+        :format(cflags, flags, env_flags "CFLAGS"),
         {
             description = "Compile C   $out",
             deps = "gcc",
@@ -122,8 +129,8 @@
 end
 
 function gcc.rule_cxx(w, name, flags, cxxflags)
-    w:rule("cxx_"..name, ([[$cc -MMD -MT $out -MF $out.d %s %s -o $out -c $in]])
-        :format(cxxflags, flags),
+    w:rule("cxx_"..name, ([[$cc -MMD -MT $out -MF $out.d %s %s %s -o $out -c $in]])
+        :format(cxxflags, flags, env_flags "CXXFLAGS"),
         {
             description = "Compile C++ $out",
             deps = "gcc",