[SCons] Simplify treatment of sydep1.h and signal1.h

We don't actually have system-dependent versions of these headers, so just put
the templates in place directly. This is also a workaround for a SCons bug on
Cygwin.

Cherry-pick of trunk r2735.

SConstruct

@@ -52,8 +52,6 @@ if 'clean' in COMMAND_LINE_TARGETS:
     removeFile('include/cantera/base/config.h')
     removeFile('interfaces/python/setup.py')
     removeFile('ext/f2c_libs/arith.h')
-    removeFile('ext/f2c_libs/signal1.h')
-    removeFile('ext/f2c_libs/sysdep1.h')
     for name in os.listdir('.'):
         if name.endswith('.msi'):
             removeFile(name)

ext/SConscript

@@ -81,14 +81,6 @@ if env['build_with_f2c']:
         arithenv.Command('#ext/f2c_libs/arith.h', 'f2c_libs/arithchk/arithchk$PROGSUFFIX',
                          '$SOURCE > $TARGET')
 
-    headerenv = prep_f2c(env)
-    # Possibly system-dependent headers
-    headerenv.Command('#ext/f2c_libs/signal1.h', 'f2c_libs/signal1.h0',
-                      Copy('$TARGET', '$SOURCE'))
-
-    headerenv.Command('#ext/f2c_libs/sysdep1.h', 'f2c_libs/sysdep1.h0',
-                      Copy('$TARGET', '$SOURCE'))
-
     libs.append(('f2c_libs', 'c', prep_f2c))
 
     if env['BUILD_BLAS_LAPACK']:

ext/f2c_libs/.gitignore

@@ -1,3 +1 @@
 arith.h
-signal1.h
-sysdep1.h