Fix accidental infinite loop in fuzz targets (#5103)

The `libfuzzer-sys` update in #5068 included some changes to the
`fuzz_target!` macro which caused a bare `run` function to be shadowed
by the macro-defined `run` function (changed in
rust-fuzz/libfuzzer#95) which meant that some of our fuzz targets were
infinite looping or stack overflowing as the same function was called
indefinitely. This renames the top-level `run` function to something
else in the meantime.

fuzz/fuzz_targets/differential.rs

@@ -53,10 +53,10 @@ fuzz_target!(|data: &[u8]| {
 
     // Errors in `run` have to do with not enough input in `data`, which we
     // ignore here since it doesn't affect how we'd like to fuzz.
-    drop(run(&data));
+    drop(execute_one(&data));
 });
 
-fn run(data: &[u8]) -> Result<()> {
+fn execute_one(data: &[u8]) -> Result<()> {
     STATS.bump_attempts();
 
     let mut u = Unstructured::new(data);

fuzz/fuzz_targets/instantiate-many.rs

@@ -12,10 +12,10 @@ const MAX_MODULES: usize = 5;
 fuzz_target!(|data: &[u8]| {
     // errors in `run` have to do with not enough input in `data`, which we
     // ignore here since it doesn't affect how we'd like to fuzz.
-    drop(run(data));
+    drop(execute_one(data));
 });
 
-fn run(data: &[u8]) -> Result<()> {
+fn execute_one(data: &[u8]) -> Result<()> {
     let mut u = Unstructured::new(data);
     let mut config: generators::Config = u.arbitrary()?;