Use header-only form of libfmt

Avoids problems when trying to link to static versions of libfmt.a which were
built without -fPIC.

SConstruct

@@ -1684,10 +1684,6 @@ if env['blas_lapack_libs']:
     linkLibs.extend(env['blas_lapack_libs'])
     linkSharedLibs.extend(env['blas_lapack_libs'])
 
-if env['system_fmt']:
-    linkLibs.append('fmt')
-    linkSharedLibs.append('fmt')
-
 # Store the list of needed static link libraries in the environment
 env['cantera_libs'] = linkLibs
 env['cantera_shared_libs'] = linkSharedLibs

ext/SConscript

@@ -36,30 +36,23 @@ def prep_gmock(env):
 
 def prep_fmt(env):
     localenv = prep_default(env)
-    if not env['system_fmt']:
-        localenv.Prepend(CPPPATH=Dir('#include/cantera/ext'))
-        license_files.append(('fmtlib', 'fmt/LICENSE.rst'))
-        for name in ('format.h', 'ostream.h', 'printf.h', 'core.h', 'format-inl.h', 'posix.h'):
-            build(copyenv.Command("#include/cantera/ext/fmt/" + name,
-                                  "#ext/fmt/include/fmt/" + name,
-                                  Copy('$TARGET', '$SOURCE')))
     return localenv
 
 # each element of libs is: (subdir, (file extensions), prepfunction)
 libs = [('libexecstream', ['cpp'], prep_default)]
 
-# fmtlib versions less than 5.0.0 had the source files for the library in a different folder.
-# Also, we expect system-installed versions of fmtlib >= 5.0.0 to have a library already compiled
-if LooseVersion(env['FMT_VERSION']) < LooseVersion('5.0.0'):
-    libs.append(('fmt/fmt', ['cc'], prep_fmt))
-elif not env['system_fmt']:
-    libs.append(('fmt/src', ['cc'], prep_fmt))
-
 for subdir, extensions, prepFunction in libs:
     localenv = prepFunction(env)
     objects = localenv.SharedObject(mglob(localenv, subdir, *extensions))
     libraryTargets.extend(objects)
 
+if not env['system_fmt']:
+    license_files.append(('fmtlib', 'fmt/LICENSE.rst'))
+    for name in ('format.h', 'ostream.h', 'printf.h', 'core.h', 'format-inl.h', 'posix.h'):
+        build(copyenv.Command("#include/cantera/ext/fmt/" + name,
+                              "#ext/fmt/include/fmt/" + name,
+                              Copy('$TARGET', '$SOURCE')))
+
 if env['system_sundials'] == 'n':
     localenv = prep_default(env)
     localenv.Prepend(CPPPATH=Dir('#include/cantera/ext'))

include/cantera/base/fmt.h

@@ -7,6 +7,10 @@
 //! the same name in kinetics/Group.h
 #define FMT_NO_FMT_STRING_ALIAS
 
+//! Use header-only library to avoid relocation issues with linking to the
+//! static libfmt.a
+#define FMT_HEADER_ONLY
+
 #if CT_USE_SYSTEM_FMT
   #include "fmt/format.h"
   #if defined(FMT_VERSION) && FMT_VERSION >= 40000