soong: add support for module specific lexer flags

To support module specific lexer flags, this follows the same strategy
as the yacc flags:
 - add LexProperties to the BaseCompilerProperties
 - propagate those flags to the generator generation (i.e. genLex)
 - add a placeholder for custom flags
 - replace the placeholder with the concatenated flags

This might not support escaping very well, but I figured that this is a
very edge case. Support for escaping etc. could be added later on.

Bug: 159682555
Signed-off-by: Matthias Maennich <maennich@google.com>
Change-Id: I31a3b783bb05213fe1621191031952b41b318103
diff --git a/cc/builder.go b/cc/builder.go
index f2bab8c..9f20b87 100644
--- a/cc/builder.go
+++ b/cc/builder.go
@@ -361,6 +361,7 @@
 	protoOptionsFile bool
 
 	yacc *YaccProperties
+	lex  *LexProperties
 }
 
 type Objects struct {