doc: add MSVC and GNUC options

Documentation/Building.md

@@ -76,6 +76,7 @@ $ make verify # Optional
 ```
 
 ## CMake Variables
+General options:
 ```
 # Type of the library to build (SHARED or STATIC)
 # Default is: SHARED for MSVC, otherwise BOTH
@@ -124,6 +125,26 @@ EVENT__FORCE_KQUEUE_CHECK:BOOL=OFF
 # Build documentation with doxygen
 EVENT__DOXYGEN:BOOL=OFF
 ```
+MSVC specific options:
+```
+# Link static runtime libraries.
+# Defaults to ON if EVENT_LIBRARY_TYPE is equal to "STATIC", otherwise OFF
+EVENT__MSVC_STATIC_RUNTIME:BOOL
+```
+GNUC specific options:
+```
+# Disable verbose warnings with GCC
+EVENT__DISABLE_GCC_WARNINGS:BOOL=OFF
+
+# Enable compiler security checks
+EVENT__ENABLE_GCC_HARDENING:BOOL=OFF
+
+# Enable gcc function sections
+EVENT__ENABLE_GCC_FUNCTION_SECTIONS:BOOL=OFF
+
+# Make all GCC warnings into errors
+EVENT__ENABLE_GCC_WARNINGS:BOOL=OFF
+```
 __More variables can be found by running `cmake -LAH <sourcedir_path>`__
 
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