system_libs.py: Combine duplicate code blocks. NFC (#16096)

Author: sbc100

tools/system_libs.py

@@ -917,8 +917,7 @@ def get_files(self):
 
     libc_files += files_in_path(
         path='system/lib/libc/musl/src/linux',
-        filenames=['getdents.c'])
-
+        filenames=['getdents.c', 'gettid.c'])
     libc_files += files_in_path(
         path='system/lib/libc/musl/src/env',
         filenames=['__environ.c', 'getenv.c', 'putenv.c', 'setenv.c', 'unsetenv.c'])
@@ -935,10 +934,6 @@ def get_files(self):
         path='system/lib/libc/musl/src/ldso',
         filenames=['dlerror.c', 'dlsym.c', 'dlclose.c'])
 
-    libc_files += files_in_path(
-        path='system/lib/libc/musl/src/linux',
-        filenames=['gettid.c'])
-
     libc_files += files_in_path(
         path='system/lib/libc/musl/src/signal',
         filenames=[