build: fix build with byacc

We apparently broke byacc support in the switch to meson.

byacc only supports short option names. And to make things fun, bison
only supports long option for `--defines`.

Fixes: https://github.com/xkbcommon/libxkbcommon/issues/133
Signed-off-by: Ran Benita <ran@unusedvar.com>

meson.build

@@ -135,13 +135,26 @@ have_version_script = cc.links(
 
 # libxkbcommon.
 # Note: we use some yacc extensions, which work with either GNU bison
-# (preferred) or byacc. Other yacc's may or may not work.
-yacc = find_program('bison', 'win_bison', 'byacc')
-yacc_gen = generator(
-    yacc,
-    output: ['@BASENAME@.c', '@BASENAME@.h'],
-    arguments: ['@INPUT@', '--defines=@OUTPUT1@', '--output=@OUTPUT0@', '-p _xkbcommon_'],
-)
+# (preferred) or byacc (with backtracking enabled).
+bison = find_program('bison', 'win_bison', required: false)
+if bison.found()
+    yacc_gen = generator(
+        bison,
+        output: ['@BASENAME@.c', '@BASENAME@.h'],
+        arguments: ['@INPUT@', '--defines=@OUTPUT1@', '--output=@OUTPUT0@', '-p _xkbcommon_'],
+    )
+else
+    byacc = find_program('byacc', required: false)
+    if byacc.found()
+        yacc_gen = generator(
+            byacc,
+            output: ['@BASENAME@.c', '@BASENAME@.h'],
+            arguments: ['@INPUT@', '-H', '@OUTPUT1@', '-o', '@OUTPUT0@', '-p _xkbcommon_'],
+        )
+    else
+        error('Could not find a compatible YACC program (bison or byacc)')
+    endif
+endif
 libxkbcommon_sources = [
     'src/compose/parser.c',
     'src/compose/parser.h',