Enable optimization on nacl-armhf with Saigo but limit the amount of optimization passes

Author: illwieckz

cmake/DaemonFlags.cmake

@@ -401,12 +401,28 @@ else()
 	endif()
 
 	if (YOKAI_TARGET_SYSTEM_NACL AND YOKAI_CXX_COMPILER_SAIGO AND YOKAI_TARGET_ARCH_ARMHF)
-		# Saigo produces broken arm builds when optimizing them.
+		# Saigo produces broken ARM builds when optimizing them.
 		# See: https://github.com/Unvanquished/Unvanquished/issues/3297
-		# When setting this clang-specific option, we don't have to care
-		# about the ordering of -O options that may be introduced,
-		# all -O options added to the command line are ignored.
-		set_c_cxx_flag("-Xclang -disable-llvm-passes")
+		# Above limit 53696, the produced Unvanquished cgame is corrupted.
+		# Under limit 21000 (approximation), the performance is not fully recovered.
+		# 50000 is selected as a high value with a fair margin.
+		# Set -1 (unlimited passes) to unlock breakage.
+		set(SAIGO_OPT_PASS_LIMIT 50000)
+		set(SAIGO_OPT_PASS_LIMIT_FLAG "-mllvm -opt-pass-limit=${SAIGO_OPT_PASS_LIMIT}")
+
+		check_CXX_compiler_flag("${SAIGO_OPT_PASS_LIMIT_FLAG}" FLAG_OPT_PASS_LIMIT)
+
+		if (FLAG_OPT_PASS_LIMIT)
+			set_c_cxx_flag("${SAIGO_OPT_PASS_LIMIT_FLAG}")
+			# The flag may be used on compilation steps not consuming LLVM backend options.
+			set_c_cxx_flag("-Wno-unused-command-line-argument")
+		else()
+			# Old Saigo builds don't implement the -opt-pass-limit option.
+			# When setting the following clang-specific option, we don't have
+			# to care about the ordering of -O options that may be introduced,
+			# all -O options added to the command line are ignored.
+			set_c_cxx_flag("-Xclang -disable-llvm-passes")
+		endif()
 	endif()
 
 	# Extra debug flags.