Search notes:

gcc -dM

-dM prints macro definitions.
In order to use -dM , the -E option must be specified, too. Otherwise, it's apparently interpreted as -fdump-rtl-mach.

Printing predefined macros

The -dM option can be used to print the predefined macros: 
echo | gcc -E -dM -x c - | sort
Github repository about-gcc, path: /options/d/M-predefined-macros

Another example

What was I thinking here? 
//
//     -dM: 
//         Generate a list of ‘#define’ directives for all the macros defined
//         during the execution of the preprocessor, including predefined macros.
//
//         Must be invoked with -E because otherwise would be interpreted as
//         synonym for -fdump-rtl-mach
// 
//   gcc -E -dM M.c
//   gcc -E -dM M.c | grep    TQ84
//   gcc -E -dM M.c | grep -v TQ84
//
#define TQ84_FOO foo
#define TQ84_BAR
Github repository about-gcc, path: /options/d/M.c

See also

GCC options
Possibly predefined preprocessor macros

Index

Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 8 attempt to write a readonly database in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php:78 Stack trace: #0 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(78): PDOStatement->execute(Array) #1 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(30): insert_webrequest_('/notes/developm...', 1759398281, '216.73.216.42', 'Mozilla/5.0 App...', NULL) #2 /home/httpd/vhosts/renenyffenegger.ch/httpsdocs/notes/development/languages/C-C-plus-plus/GCC/options/dM(72): insert_webrequest() #3 {main} thrown in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php on line 78