Fix terminfo detection in libncurses

Bug: android/ndk#1565

1. Mac has a case-insensitive file system where the subdirs of
   /usr/share/terminfo are ascii values ('78') instead of letters ('x').
   The ncurses configure script detects this based on the filesystem
   it's running on.  Unfortunately, the android build servers run on a
   separate volume with a case-sensitive file system, breaking this
   detection.  Override by setting --disable-mixed-case config flag.

2. Set --with-default-terminfo-dir to always read from
   /usr/share/terminfo for all platforms.

Test: lldb.sh opens successfully on a Mac
Change-Id: I1b9da0093be44331b80b6b21cbe3254de8f53408

builders.py

@@ -662,9 +662,13 @@ class LibNcursesBuilder(base_builders.AutoconfBuilder, base_builders.LibInfo):
 
     @property
     def config_flags(self) -> List[str]:
-        return super().config_flags + [
+        flags = super().config_flags + [
             '--with-shared',
+            '--with-default-terminfo-dir=/usr/share/terminfo',
         ]
+        if self._config.target_os.is_darwin:
+            flags.append('--disable-mixed-case')
+        return flags
 
     @property
     def _lib_names(self) -> List[str]: