Extended lfsr_mount to accept mount flags

This has been a long-time coming, mount flags are just too useful for
configuring a filesystem at runtime.

Currently this is limited to LFS_M_RDONLY and LFS_M_CKPROGS, but there
are a few more planned in the future:

  LFS_M_RDWR     = 0x0000, // Mount the filesystem as read and write
  LFS_M_RDONLY   = 0x0001, // Mount the filesystem as readonly
  LFS_M_STRICT*  = 0x0002, // Error if on-disk config does not match
  LFS_M_FORCE*   = 0x0004, // Ignore compat flags, mount readonly
  LFS_M_FORCEWITHRECKLESSABANDON*
                 = 0x0008, // Ignore compat flags, mount read write

  LFS_M_CKPROGS  = 0x0010, // Check progs by reading back progged data
  LFS_M_CKREADS* = 0x0020, // Check reads via checksums

  * Hypothetical

As a convenience, we also return mount flags in the struct lfs_fsinfo's
flags field as their relevant LFS_I_* variants. Though only to match
statvfs, and only because it's cheap, littlefs's API is low-level and we
should expect users to know what flags they passed to lfsr_mount.

As for the new mount flags:

- LFS_M_RDONLY - For consistency with existing APIs, this just asserts
  on write operations, which makes it a bit useless... But the info flag
  LFS_I_RDONLY may be useful for falling back to a readonly mode if
  we encounter on-disk compat issues.

  At least if implement the theoretical LFS_UNTRUSTED_USER mode
  LFS_M_RDONLY could become a runtime error.

- LFS_M_RDWR - This really just exists to compliment LFS_M_RDONLY and to
  match LFS_O_RDONLY/LFS_O_RDWR. It's just an alias for 0, and I don't
  think there will ever be a reason to make it non-0 (but I can always
  be wrong!).

- LFS_M_CKPROGS - This replaces the check_progs config option and avoids
  using a full byte to store a bool.

  We should probably also have a compile-time option to compile this out
  (LFS_NO_CKPROGS?), but that's a future thing to do.

This ended up adding a surprising bit of code, considering we're just
moving flags around, and noise in lfs_alloc added a bit of stack again:

           code          stack
  before: 35880           2672
  after:  35932 (+0.1%)   2680 (+0.3%)

tests/test_exhaustion.toml

@@ -32,7 +32,7 @@ defines.BADBLOCK_BEHAVIOR = [
     'LFS_EMUBD_BADBLOCK_ERASENOOP',
 ]
 # we need prog checking to detect read errors
-defines.CHECK_PROGS = 'BADBLOCK_BEHAVIOR >= LFS_EMUBD_BADBLOCK_READERROR'
+defines.CKPROGS = 'BADBLOCK_BEHAVIOR >= LFS_EMUBD_BADBLOCK_READERROR'
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256]
 defines.SEED = 42
 fuzz = 'SEED'
@@ -56,7 +56,10 @@ code = '''
         // run the test
         lfs_t lfs;
         lfsr_format(&lfs, &cfg) => 0;
-        lfsr_mount(&lfs, &cfg) => 0;
+        lfsr_mount(&lfs,
+                LFS_M_RDWR
+                    | ((CKPROGS) ? LFS_M_CKPROGS : 0),
+                &cfg) => 0;
 
         // set up a simulation to compare against
         lfs_size_t *sim = malloc(N*sizeof(lfs_size_t));
@@ -231,7 +234,7 @@ defines.BADBLOCK_BEHAVIOR = [
     'LFS_EMUBD_BADBLOCK_ERASENOOP',
 ]
 # we need prog checking to detect read errors
-defines.CHECK_PROGS = 'BADBLOCK_BEHAVIOR >= LFS_EMUBD_BADBLOCK_READERROR'
+defines.CKPROGS = 'BADBLOCK_BEHAVIOR >= LFS_EMUBD_BADBLOCK_READERROR'
 defines.N = [1, 2, 4, 8, 16, 32, 64]
 defines.SIZE = [
     '0',
@@ -265,7 +268,10 @@ code = '''
         // run the test
         lfs_t lfs;
         lfsr_format(&lfs, &cfg) => 0;
-        lfsr_mount(&lfs, &cfg) => 0;
+        lfsr_mount(&lfs,
+                LFS_M_RDWR
+                    | ((CKPROGS) ? LFS_M_CKPROGS : 0),
+                &cfg) => 0;
 
         // set up a simulation to compare against
         lfs_size_t *sim = malloc(N*sizeof(lfs_size_t));
@@ -503,7 +509,7 @@ defines.BADBLOCK_BEHAVIOR = [
     'LFS_EMUBD_BADBLOCK_ERASENOOP',
 ]
 # we need prog checking to detect read errors
-defines.CHECK_PROGS = 'BADBLOCK_BEHAVIOR >= LFS_EMUBD_BADBLOCK_READERROR'
+defines.CKPROGS = 'BADBLOCK_BEHAVIOR >= LFS_EMUBD_BADBLOCK_READERROR'
 defines.SIZE = [
     'FILE_BUFFER_SIZE/2',
     '2*FILE_BUFFER_SIZE',
@@ -546,7 +552,10 @@ code = '''
         // run the test
         lfs_t lfs;
         lfsr_format(&lfs, &cfg) => 0;
-        lfsr_mount(&lfs, &cfg) => 0;
+        lfsr_mount(&lfs,
+                LFS_M_RDWR
+                    | ((CKPROGS) ? LFS_M_CKPROGS : 0),
+                &cfg) => 0;
 
         // create a file
         lfsr_file_t file;
@@ -683,7 +692,7 @@ defines.BADBLOCK_BEHAVIOR = [
     'LFS_EMUBD_BADBLOCK_ERASENOOP',
 ]
 # we need prog checking to detect read errors
-defines.CHECK_PROGS = 'BADBLOCK_BEHAVIOR >= LFS_EMUBD_BADBLOCK_READERROR'
+defines.CKPROGS = 'BADBLOCK_BEHAVIOR >= LFS_EMUBD_BADBLOCK_READERROR'
 defines.N = [1, 2, 4, 8, 16, 32, 64]
 defines.SIZE = [
     '0',
@@ -717,7 +726,10 @@ code = '''
         // run the test
         lfs_t lfs;
         lfsr_format(&lfs, &cfg) => 0;
-        lfsr_mount(&lfs, &cfg) => 0;
+        lfsr_mount(&lfs,
+                LFS_M_RDWR
+                    | ((CKPROGS) ? LFS_M_CKPROGS : 0),
+                &cfg) => 0;
 
         // set up a simulation to compare against
         lfs_size_t *sim = malloc(N*sizeof(lfs_size_t));
@@ -1096,7 +1108,7 @@ defines.BADBLOCK_BEHAVIOR = [
     'LFS_EMUBD_BADBLOCK_ERASENOOP',
 ]
 # we need prog checking to detect read errors
-defines.CHECK_PROGS = 'BADBLOCK_BEHAVIOR >= LFS_EMUBD_BADBLOCK_READERROR'
+defines.CKPROGS = 'BADBLOCK_BEHAVIOR >= LFS_EMUBD_BADBLOCK_READERROR'
 defines.N = [1, 2, 4, 8, 16, 32, 64]
 defines.SIZE = [
     '0',
@@ -1130,7 +1142,10 @@ code = '''
         // run the test
         lfs_t lfs;
         lfsr_format(&lfs, &cfg) => 0;
-        lfsr_mount(&lfs, &cfg) => 0;
+        lfsr_mount(&lfs,
+                LFS_M_RDWR
+                    | ((CKPROGS) ? LFS_M_CKPROGS : 0),
+                &cfg) => 0;
 
         // set up a simulation to compare against
         lfs_size_t *sim = malloc(N*sizeof(lfs_size_t));