Increase fortification level

Newer versions of GCC and Clang support _FORTIFY_SOURCE=3 which
increases code safety by providing better size checks

For reference see
https://developers.redhat.com/articles/2023/02/06/how-improve-application-security-using-fortifysource3

CMakeLists.txt

@@ -129,7 +129,7 @@ target_compile_definitions(btop PRIVATE
   _FILE_OFFSET_BITS=64
   _GLIBCXX_ASSERTIONS _LIBCPP_ENABLE_ASSERTIONS=1
   # Only has an effect with optimizations enabled
-  $<$<NOT:$<CONFIG:Debug>>:_FORTIFY_SOURCE=2>
+  $<$<NOT:$<CONFIG:Debug>>:_FORTIFY_SOURCE=3>
 )
 
 target_include_directories(btop SYSTEM PRIVATE include)

Makefile

@@ -172,7 +172,7 @@ override GOODFLAGS := $(foreach flag,$(TESTFLAGS),$(strip $(shell echo "int main
 override REQFLAGS   := -std=c++20
 WARNFLAGS			:= -Wall -Wextra -pedantic
 OPTFLAGS			:= -O2 -ftree-vectorize -flto=$(LTO)
-LDCXXFLAGS			:= -pthread -D_FORTIFY_SOURCE=2 -D_GLIBCXX_ASSERTIONS -D_FILE_OFFSET_BITS=64 $(GOODFLAGS) $(ADDFLAGS)
+LDCXXFLAGS			:= -pthread -D_FORTIFY_SOURCE=3 -D_GLIBCXX_ASSERTIONS -D_FILE_OFFSET_BITS=64 $(GOODFLAGS) $(ADDFLAGS)
 override CXXFLAGS	+= $(REQFLAGS) $(LDCXXFLAGS) $(OPTFLAGS) $(WARNFLAGS)
 override LDFLAGS	+= $(LDCXXFLAGS) $(OPTFLAGS) $(WARNFLAGS)
 INC					:= $(foreach incdir,$(INCDIRS),-isystem $(incdir)) -I$(SRCDIR)