Output of source_flattener.py does not compile

[arahlin]

Running source_flattener.py on the latest erfa release (2.0.0) creates the following errors when attempting to compile the result (this is with Apple clang 12.0 on OSX 10.15):

gcc -c -pedantic -Wall -O3 -g -fPIC -I. erfa.c -o erfa.o
In file included from erfa.c:1:
./erfa.h:634:21: error: unknown type name 'eraLEAPSECOND'
int eraDatini(const eraLEAPSECOND *builtin, int n_builtin,
                    ^
./erfa.h:635:15: error: unknown type name 'eraLEAPSECOND'
              eraLEAPSECOND **leapseconds);
              ^
./erfa.h:624:2: error: unterminated conditional directive
#ifndef _ERFA_DAT_EXTRA_H
 ^
./erfa.h:1:2: error: unterminated conditional directive
#ifndef ERFAHDEF
 ^
erfa.c:11911:10: error: use of undeclared identifier 'PACKAGE_VERSION'
  return PACKAGE_VERSION;
         ^
erfa.c:11916:10: error: use of undeclared identifier 'PACKAGE_VERSION_MAJOR'
  return PACKAGE_VERSION_MAJOR;
         ^
erfa.c:11921:10: error: use of undeclared identifier 'PACKAGE_VERSION_MINOR'
  return PACKAGE_VERSION_MINOR;
         ^
erfa.c:11926:10: error: use of undeclared identifier 'PACKAGE_VERSION_MICRO'
  return PACKAGE_VERSION_MICRO;
         ^
erfa.c:11931:10: error: use of undeclared identifier 'SOFA_VERSION'
  return SOFA_VERSION;
         ^
erfa.c:15638:21: error: use of undeclared identifier 'DBL_EPSILON'
   if ( (f-1.0) >= -DBL_EPSILON/4.0 ) {
                    ^
erfa.c:15645:13: error: use of undeclared identifier 'DBL_EPSILON'
      if ( -DBL_EPSILON/2.0 < f ) {
            ^
11 errors generated.
make[1]: *** [erfa.o] Error 1
make: *** [erfa] Error 2

It looks like the flattener creates a header file with the erfaextra.h and erfadatextra.h headers copied in the wrong order (the latter depends on the former), and with missing #endif directives (or without stripping the existing directives from the headers first). The erfa.c source file includes the version and leapsecond code, but also includes the testing code in t_erfa_c_extra.c. The source file is also missing the #include <float.h> that's required in jd2cal.c.