Fix bugs in generate_compiler_commands.sh

Invoke env from its standard location.  If you're going to hard-code a
non-standard env location to find bash, you may as well hard-code a bash
location.

Generate the top-level compile_commands.json from the test suite so that
syntax highlighting in the RTOS works again.

scripts/generate_compile_commands.sh

diff --git a/scripts/generate_compile_commands.sh b/scripts/generate_compile_commands.sh
index cc75a0b..a05cbee 100755
--- a/scripts/generate_compile_commands.sh
+++ b/scripts/generate_compile_commands.sh
@@ -1,4 +1,4 @@
-#!/bin/env bash
+#!/usr/bin/env bash
 
 # Generate compile commands files for all known projects in this repo
 
@@ -11,7 +11,11 @@
 
 echo "Using SDK=$SDK"
 
-for dir in tests tests.extra/*/ ex*/[[:digit:]]* ; do 
+# Generate compile_commands.json for all of the extra tests and examples.
+for dir in tests.extra/*/ ex*/[[:digit:]]* ; do
     echo Generating compile_commands.json for $dir
     (cd $dir && xmake f --sdk="${SDK}" && xmake project -k compile_commands)
 done
+
+# Generate the top-level compile-commands.json
+cd tests && xmake f --sdk="${SDK}" && xmake project -k compile_commands ..