Makefile: Switch to C++20

Makefile

@@ -1,7 +1,7 @@
 
-
-CXXFLAGS=-std=c++17 -O0 -g -no-pie -pipe -MMD -Wall -Wextra
-RELEASE_CXXFLAGS=-std=c++17 -O3 -pipe -MMD -Wall -Wextra
+CPPSTD=c++20
+CXXFLAGS=-std=$(CPPSTD) -O0 -g -no-pie -pipe -MMD -Wall -Wextra
+RELEASE_CXXFLAGS=-std=$(CPPSTD) -O3 -pipe -MMD -Wall -Wextra
 LDFLAGS=-lsqlite3 -lpthread -lcrypto -lstdc++fs
 INCLUDEFLAGS=-I submodules/sqlitemoderncpp/hdr -I submodules/cpp-httplib -I submodules/qssb.h
 
@@ -35,7 +35,7 @@ GTEST_DIR = /home/data/SOURCES/gtest/googletest
 
 GTESTS_TESTDIR = ./tests/
 
-GTEST_CXXFLAGS=-std=c++17 -isystem $(GTEST_DIR)/include -I$(GTEST_DIR) -g -O0 -pipe -Wall -Wextra
+GTEST_CXXFLAGS=-std=$(CPPSTD) -isystem $(GTEST_DIR)/include -I$(GTEST_DIR) -g -O0 -pipe -Wall -Wextra
 GTEST_LDFLAGS=-lsqlite3 -g -O0 -lpthread -lcrypto -lstdc++fs
 GTEST_OBJECTS=$(filter-out qswiki.o, $(WIKIOBJECTS))