auto merge of #19117 : jmesmon/rust/mk-cfg-suffix, r=cmr

Right now we'll end up globbing them into the accepted targets and (ever worse) they will override the make variables of real target files because we `include`d everything in that directory.

As a side effect, editors get a better hint on file types.

configure

@@ -893,7 +893,10 @@ CFG_PREFIX=${CFG_PREFIX%/}
 CFG_MANDIR=${CFG_MANDIR%/}
 CFG_HOST="$(echo $CFG_HOST | tr ',' ' ')"
 CFG_TARGET="$(echo $CFG_TARGET | tr ',' ' ')"
-CFG_SUPPORTED_TARGET="$(ls ${CFG_SRC_DIR}mk/cfg)"
+CFG_SUPPORTED_TARGET=""
+for target_file in ${CFG_SRC_DIR}mk/cfg/*.mk; do
+  CFG_SUPPORTED_TARGET="${CFG_SUPPORTED_TARGET} $(basename "$target_file" .mk)"
+done
 
 # copy host-triples to target-triples so that hosts are a subset of targets
 V_TEMP=""

mk/platform.mk

@@ -113,7 +113,7 @@ $(foreach cvar,CC CXX CPP CFLAGS CXXFLAGS CPPFLAGS, \
 
 CFG_RLIB_GLOB=lib$(1)-*.rlib
 
-include $(wildcard $(CFG_SRC_DIR)mk/cfg/*)
+include $(wildcard $(CFG_SRC_DIR)mk/cfg/*.mk)
 
 # The -Qunused-arguments sidesteps spurious warnings from clang
 define FILTER_FLAGS