[libc++][test][NFC] Clang-format <regex> tests

There is possibly upcoming overhaul for `<regex>`. It would be easier to
modify the test files if they are clang-formatted.

Some files are manually adjusted.

Adds clang-format off/on comments to avoid line break:
- libcxx/test/std/re/re.regex/re.regex.construct/awk_oct.pass.cpp
- libcxx/test/std/re/re.regex/re.regex.construct/deduct.verify.cpp

Adds new lines to avoid ugly grouping for `=`:
- libcxx/test/std/re/re.const/re.matchflag/match_flag_type.pass.cpp
- libcxx/test/std/re/re.const/re.synopt/syntax_option_type.pass.cpp

Author: frederick-vs-ja

libcxx/test/std/re/re.alg/re.alg.match/awk.pass.cpp

@@ -22,16 +22,15 @@
 #include "test_macros.h"
 
 #if TEST_STD_VER < 14
-#error
+#  error
 #endif
 
-int main(int, char**)
-{
-    {
-        std::smatch m;
-        std::regex re{"*"};
-        std::regex_match(std::string("abcde"), m, re);
-    }
+int main(int, char**) {
+  {
+    std::smatch m;
+    std::regex re{"*"};
+    std::regex_match(std::string("abcde"), m, re);
+  }
 
   return 0;
 }