The ndk-gdb script relies on setting the adb path, either by setting it as
an environment variable or
explicitly as a parameter of the script call.
Thus, there are two probable solutions:
1) set the PATH environment variable to point out your android sdk tools
folder (e.g. "export PATH=$PATH:<your_android_sdk_path_here>/tools")
or
2) invoke the ndk-gdb command with the path to the adb as a parameter (e.g.
: "ndk-gdb --adb=<your_android_sdk_path_here>/tools/adb")
keep in mind that the 1) solution will only work for your current terminal
session. If you want to persist this new PATH value, you must set it up
in the ~.MacOSX/environment.plist.