llvm-context: alloca at the function entry if possible (#283)

Closes  #48

Change the code size test to no longer emit debug info as to get a more
accurate picture.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/integration/codesize.json

@@ -1,10 +1,10 @@
 {
-  "Baseline": 1365,
-  "Computation": 2710,
-  "DivisionArithmetics": 9672,
-  "ERC20": 19131,
-  "Events": 2123,
-  "FibonacciIterative": 1964,
-  "Flipper": 2590,
-  "SHA1": 8918
+  "Baseline": 950,
+  "Computation": 2222,
+  "DivisionArithmetics": 8802,
+  "ERC20": 17602,
+  "Events": 1628,
+  "FibonacciIterative": 1485,
+  "Flipper": 2082,
+  "SHA1": 8230
 }