Remove dependancies on gcc/perl etc. This saves a bunch of stats and

build/SConscript.main

Index: build/SConscript.main
diff --git a/build/SConscript.main b/build/SConscript.main
index d2fa3312b219afb3a66bb4f3837d85a4eb973184..ba0a267ada18ecf76131e3e865a676394e462933 100644
--- a/build/SConscript.main
+++ b/build/SConscript.main
@@ -338,6 +338,11 @@ linux_env = root_env.Clone()
 linux_env.Tool('target_platform_linux')
 linux_env.Tool('yacc')
 
+# By default scons will depend on the first path element for any command line.
+# For example, it will resolve 'gcc' with $PATH and depend on that for any
+# action which runs gcc. This disables this behaviour:
+linux_env['IMPLICIT_COMMAND_DEPENDENCIES'] = False
+
 # TODO(bradnelson): this is needed for now because target_platform_linux has
 # OS_LINUX defined in a weird way.
 linux_env.FilterOut(CPPDEFINES = ['OS_LINUX=OS_LINUX'])