Added gcc help page

_commands/basics/gcc.md

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+---
+---
+
+gcc
+---
+`gcc` is a GNU compiler for C.
+
+~~~ bash
+$ gcc hello.c
+$ ./a.out
+$ gcc hello.c -o hello
+$ ./hello
+~~~
+
+<!--more-->
+
+### Useful Options / Examples
+
+### `gcc <filename>`
+Compiles c files. The executable file generated is called ``a.out``.
+
+~~~bash
+$ gcc hello.c
+$ ./a.out
+$ Hello World!
+~~~ 
+
+### `gcc <filename> -o <exec_name>`
+Compiles c files and creates an executable with the specified name, i.e the argument passed after `-o`.
+
+~~~bash
+$ gcc hello.c -o helloWorld
+$ ./helloWorld
+$ Hello World!
+~~~
+
+### `gcc -Wall`
+`-Wall` enables all commonly used compiler flags. It is reccomended to always use this flag. 
+This will make sure you have a 'clean' compile.
+If we have the following file `sum.c` - (Note that the variable _c_ is unused)
+
+```c
+#include <stdio.h>
+
+int main(void) {
+	int c = 1;
+	print f("1 + 1 is %d\n", 2);
+	return 0;
+}
+```
+
+Running without `-Wall` gives us no error.
+
+~~~bash
+$ gcc sum.c -o sum
+$ ./sum
+$ 1 + 1 is 2
+~~~
+
+However, using the flag we get a __warning__ - 
+
+~~~bash
+$ gcc -Wall sum.c -o sum
+sum.c: In function ‘main’:
+sum.c:4:6: warning: unused variable ‘c’ [-Wunused-variable]
+  int c = 1;
+      ^
+
+~~~
+
+
+### `gcc -Werror`
+`-Werror` converts all warings to errors.
+
+~~~bash
+$ gcc -Wall -Werror sum.c -o sum
+sum.c: In function ‘main’:
+sum.c:4:6: error: unused variable ‘c’ [-Werror=unused-variable]
+  int c = 1;
+      ^
+cc1: all warnings being treated as errors
+~~~
+
+### `gcc -O`
+The `-O` flag is used to specify different optimization options.
+`O0` is default. `O1 O2 O3` respectively optimize for execution time and space, 3 being the fastest.
+`Os` optimizes for space.
+
+
+### `gcc -d`
+The `-d` flag produces debugging information.