configure: verify presence of msgfmt instead of relying on it

NEWS.md

@@ -18,6 +18,9 @@
   line feed) again instead of just `\n` (line feed).
 * build system: an error message is output if a command to execute is not
   found instead of silently failing.
+* build system: in addition to looking for the `gettext` C function and
+  library, `configure` now also verifies the presence of the `msgfmt` program
+  instead of simply relying on it.
 
 
 # Version 20.0.0 "I Am The Sun" 2018-01-15

Rakefile

@@ -309,7 +309,7 @@ if $building_for[:windows]
 end
 
 rule '.mo' => '.po' do |t|
-  runq "msgfmt", t.source, "msgfmt -c -o #{t.name} #{t.sources.join(" ")}"
+  runq "msgfmt", t.source, "#{c(:MSGFMT)} -c -o #{t.name} #{t.sources.join(" ")}"
 end
 
 if !c(:LCONVERT).blank?

ac/translations.m4

@@ -12,6 +12,11 @@ if test "x$with_gettext" != "xno"; then
                  [ gettext_found=no ],
                  [ -liconv ])
   fi
+
+  AC_PATH_PROG(MSGFMT, msgfmt,, $PATH)
+  if test -z "$MSGFMT"; then
+    gettext_found=no
+  fi
 fi
 
 if test x"$gettext_found" = xyes ; then

build-config.in

@@ -58,6 +58,7 @@ install_sh_PROGRAM = $(install_sh) -c
 install_sh_SCRIPT = $(install_sh) -c
 LCONVERT = @LCONVERT@
 LD = @LD@
+MSGFMT = @MSGFMT@
 MOC = @MOC@
 OBJEXT = @OBJEXT@
 PANDOC = @PANDOC@