Patch from https://github.com/aristocratos/btop/pull/648/files.
Allows to disable setting -D_FORTIFY_SOURCE in the build system,
so the fortification level can be configured freely in make.conf.

Bug: https://bugs.gentoo.org/898148

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -41,6 +41,7 @@ option(BTOP_LTO "Enable LTO" ON)
 option(BTOP_USE_MOLD "Use mold to link btop" OFF)
 option(BTOP_PEDANTIC "Enable a bunch of additional warnings" OFF)
 option(BTOP_WERROR "Compile with warnings as errors" OFF)
+option(BTOP_FORTIFY "Detect buffer overflows with _FORTIFY_SOURCE=3" ON)
 option(BTOP_GPU "Enable GPU support" ON)
 cmake_dependent_option(BTOP_RSMI_STATIC "Link statically to ROCm SMI" OFF "BTOP_GPU" OFF)
 
@@ -112,7 +113,7 @@ target_compile_definitions(btop PRIVATE
   _FILE_OFFSET_BITS=64
   $<$<CONFIG:Debug>:_GLIBCXX_ASSERTIONS _LIBCPP_ENABLE_ASSERTIONS=1>
   # Only has an effect with optimizations enabled
-  $<$<NOT:$<CONFIG:Debug>>:_FORTIFY_SOURCE=2>
+  $<$<AND:$<NOT:$<CONFIG:Debug>>,$<BOOL:${BTOP_FORTIFY}>>:_FORTIFY_SOURCE=3>
 )
 
 target_include_directories(btop SYSTEM PRIVATE include)
--- a/Makefile
+++ b/Makefile
@@ -50,6 +50,11 @@ ifeq ($(GPU_SUPPORT),true)
 	override ADDFLAGS += -DGPU_SUPPORT
 endif
 
+FORTIFY_SOURCE ?= true
+ifeq ($(FORTIFY_SOURCE),true)
+	override ADDFLAGS += -D_FORTIFY_SOURCE=3
+endif
+
 #? Compiler and Linker
 ifeq ($(shell $(CXX) --version | grep clang >/dev/null 2>&1; echo $$?),0)
 	override CXX_IS_CLANG := true
@@ -174,7 +179,7 @@ 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_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)