Everywhere: Re-format with clang-format-11

Compared to version 10 this fixes a bunch of formatting issues, mostly
around structs/classes with attributes like [[gnu::packed]], and
incorrect insertion of spaces in parameter types ("T &"/"T &&").
I also removed a bunch of // clang-format off/on and FIXME comments that
are no longer relevant - on the other hand it tried to destroy a couple of
neatly formatted comments, so I had to add some as well.

Libraries/LibC/regex.h

@@ -101,6 +101,7 @@ enum __RegexAllFlags {
     __Regex_Last = __Regex_SkipTrimEmptyMatches
 };
 
+// clang-format off
 // Values for the cflags parameter to the regcomp() function:
 #define REG_EXTENDED __Regex_Extended                // Use Extended Regular Expressions.
 #define REG_ICASE __Regex_Insensitive                // Ignore case in match.
@@ -114,6 +115,7 @@ enum __RegexAllFlags {
 
 //static_assert (sizeof(FlagsUnderlyingType) * 8 >= regex::POSIXFlags::Last << 1), "flags type too small")
 #define REG_SEARCH __Regex_Last << 1
+// clang-format on
 
 int regcomp(regex_t*, const char*, int);
 int regexec(const regex_t*, const char*, size_t, regmatch_t[], int);