Build with the "read-only relocation" hardening linker flag

Summary: Improve binary security by enabling a hardening linker flag.

Test Plan:
Patch already used on Debian.

Tested locally by @Gallaecio as well.

Reviewed By: LudovicRousseau
Trac Tickets: #4894

Differential Revision: https://code.wildfiregames.com/D1123
This was SVN commit r20896.

binaries/data/mods/public/gui/credits/texts/programming.json

@@ -225,6 +225,7 @@
 			{"nick": "trompetin17", "name": "Juan Guillermo"},
 			{"nick": "user1", "name": "A. C."},
 			{"nick": "usey11"},
+			{"nick": "vincent_c", "name": "Vincent Cheng"},
 			{"nick": "vladislavbelov", "name": "Vladislav Belov"},
 			{"nick": "vts", "name": "Jeroen DR"},
 			{"nick": "WhiteTreePaladin", "name": "Brian Ashley"},

build/premake/premake4.lua

@@ -271,7 +271,7 @@ function project_set_build_flags()
 
 				if os.is("linux") or os.is("bsd") then
 					buildoptions { "-fPIC" }
-					linkoptions { "-Wl,--no-undefined", "-Wl,--as-needed" }
+					linkoptions { "-Wl,--no-undefined", "-Wl,--as-needed", "-Wl,-z,relro" }
 				end
 
 				if arch == "x86" then

build/premake/premake5.lua

@@ -257,7 +257,7 @@ function project_set_build_flags()
 
 				if os.istarget("linux") or os.istarget("bsd") then
 					buildoptions { "-fPIC" }
-					linkoptions { "-Wl,--no-undefined", "-Wl,--as-needed" }
+					linkoptions { "-Wl,--no-undefined", "-Wl,--as-needed", "-Wl,-z,relro" }
 				end
 
 				if arch == "x86" then