vim-patch:8.2.1047: Vim9: script cannot use line continuation like :def function

Problem:    Vim9: script cannot use line continuation like in a :def function.
Solution:   Pass the getline function pointer to the eval() functions.  Use it
            for addition and multiplication operators.

5409f5d8c9

Omit source_nextline() and eval_next_non_blank(): Vim9 script only.

N/A patches for version.c:

vim-patch:8.2.1048: build failure without the eval feature

Problem:    Build failure without the eval feature.
Solution:   Add dummy typedef.

9d40c63c7d

vim-patch:8.2.1052: build failure with older compilers

Problem:    Build failure with older compilers.
Solution:   Move declaration to start of block.

7acde51832

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/quickfix.c

@@ -6958,7 +6958,7 @@ void ex_cexpr(exarg_T *eap)
   // Evaluate the expression.  When the result is a string or a list we can
   // use it to fill the errorlist.
   typval_T tv;
-  if (eval0(eap->arg, &tv, &eap->nextcmd, EVAL_EVALUATE) == FAIL) {
+  if (eval0(eap->arg, &tv, &eap->nextcmd, &EVALARG_EVALUATE) == FAIL) {
     return;
   }