added Clang UBSan support

 - allow to enable UBSan with the CONFIG+=ubsan config with qmake
 - added UBSan.supp config to suppress Qt's errors, can be enabled using
   the UBSAN_OPTIONS=suppressions=<path>/UBSan.supp env. variable

qmake/unixconf.pri

@@ -41,3 +41,24 @@ QMAKE_CXXFLAGS_WARN_ON *= \
 
 # Clang 12 still doesn't support -Wstrict-null-sentinel
 !clang: QMAKE_CXXFLAGS_WARN_ON *= -Wstrict-null-sentinel
+
+# Allow to enable UBSan with Clang
+clang:ubsan: {
+    QMAKE_CXXFLAGS += -O1
+
+    QMAKE_CXXFLAGS *= \
+        -fsanitize=undefined \
+        -fsanitize=nullability \
+        -fsanitize=float-divide-by-zero \
+        -fsanitize=unsigned-integer-overflow \
+        -fsanitize=implicit-conversion \
+        -fsanitize=local-bounds \
+
+    QMAKE_LFLAGS *= \
+        -fsanitize=undefined \
+        -fsanitize=nullability \
+        -fsanitize=float-divide-by-zero \
+        -fsanitize=unsigned-integer-overflow \
+        -fsanitize=implicit-conversion \
+        -fsanitize=local-bounds
+}

tools/configs/UBSan.supp

@@ -0,0 +1,2 @@
+implicit-integer-sign-change:qarraydata.h
+unsigned-integer-overflow:qhashfunctions.h