ui: Allow Shift-SPC to enter = in an expression

When entering `Shift-SPC` in the expression mode, enter an `=` sign
instead of a program separator (which makes no sense in an expression)

We also reached the stage where we need to switch back to optimizing
for space instead of speed.

Fixes: #1189

Signed-off-by: Christophe de Dinechin <christophe@dinechin.org>

Makefile

@@ -394,7 +394,7 @@ DBGFLAGS_debug = -g
 
 CFLAGS_debug += -Os -DDEBUG
 CFLAGS_release += $(CFLAGS_release_$(VARIANT))
-CFLAGS_release_dm42 = -O2
+CFLAGS_release_dm42 = -Os
 CFLAGS_release_dm32 = -O2
 CFLAGS_small += -Os
 CFLAGS_fast += -O2

src/user_interface.cc

@@ -4201,6 +4201,9 @@ bool user_interface::handle_editing(int key)
             if (shift)
             {
                 // Shift R/S = PRGM enters a program symbol
+                if (mode == ALGEBRAIC || mode == PARENTHESES)
+                    edit('=', ALGEBRAIC);
+                else
                     edit(L'«', PROGRAM);
                 last = 0;
                 return true;