Do not require parentheses for the 'defined' preprocessor operator

The regex that checks for preprocessor macros using the 'defined'
operator assumes that the macro that follows the operator is between
parenthesis. However, the syntax for the 'defined' operator does not
require parenthesis, at least in GNU Cpp [1] and Intel fpp [2], arguably
the two most commonly used Fortran preprocessors.

Tweak the regex by allowing the opening and closing parenthesis zero or
once.

[1] https://gcc.gnu.org/onlinedocs/gcc-10.2.0/cpp/Defined.html#Defined
[2] https://software.intel.com/content/www/us/en/develop/documentation/fortran-compiler-oneapi-dev-guide-and-reference/top/optimization-and-programming-guide/fpp-preprocessing/using-fpp-preprocessor-directives.html

Author: phil-blain

fortls/regex_patterns.py

@@ -110,7 +110,7 @@ class FortranRegularExpressions:
     FREE_OPENMP: Pattern = compile(r"[ ]*!\$OMP", I)
     FREE_FORMAT_TEST: Pattern = compile(r"[ ]{1,4}[a-z]", I)
     # Preprocessor matching rules
-    DEFINED: Pattern = compile(r"defined[ ]*\([ ]*([a-z_][a-z0-9_]*)[ ]*\)", I)
+    DEFINED: Pattern = compile(r"defined[ ]*\(?[ ]*([a-z_][a-z0-9_]*)[ ]*\)?", I)
     PP_REGEX: Pattern = compile(r"#(if |ifdef|ifndef|else|elif|endif)")
     PP_DEF: Pattern = compile(r"#(define|undef)[ ]*([\w]+)(\((\w+(,[ ]*)?)+\))?", I)
     PP_DEF_TEST: Pattern = compile(r"(![ ]*)?defined[ ]*\([ ]*([a-z0-9_]*)[ ]*\)$", I)