Fix build

```
flex -osrc/lex.yy.c src/lex.l
cc -g -c src/y.tab.c -o src/parse.o
In file included from src/parse.y:196:0:
src/lex.l: In function 'strdup0':
src/lex.l:13:16: warning: incompatible implicit declaration of built-in function 'strlen' [enabled by default]
   size_t len = strlen(s);
                ^
src/lex.l:18:5: warning: incompatible implicit declaration of built-in function 'strcpy' [enabled by default]
     strcpy(p, s);
     ^
src/lex.l: In function 'strndup0':
src/lex.l:34:5: warning: incompatible implicit declaration of built-in function 'memcpy' [enabled by default]
     memcpy(new, s, i);
     ^
In file included from src/parse.y:196:0:
src/lex.l: In function 'yylex':
src/lex.l:91:36: warning: incompatible implicit declaration of built-in function 'strlen' [enabled by default]
   yylval->str = strndup0(yytext+1, strlen(yytext)-2);
                                    ^
mkdir -p "$(dirname bin/streem)"
cc -g src/parse.o -o bin/streem
```
And I notice build-failure on windows. flex handle `-o` as `-ooutput` not `-o output`.