ThinLTO at -O0: flang does not mark -O0 functions noinline

Only clang marks every function noinline at -O0, which the ThinLTO
importer skips. flang's -O0 objects import fine, so the Fortran test needs
no -force-import-all, and the README says the limitation is clang's.

Assisted-by: Claude Code (Opus 5.5)

enzyme/Fortran/README.md

diff --git a/enzyme/Fortran/README.md b/enzyme/Fortran/README.md
index 8b5afd4..c543659 100644
--- a/enzyme/Fortran/README.md
+++ b/enzyme/Fortran/README.md
@@ -43,7 +43,7 @@
 The compile step asks ThinLTO to import the function passed to `__enzyme_autodiff`
 and the functions it calls. ThinLTO still applies its size limit to functions further
 down the call graph, and never imports functions marked `noinline` (which includes
-everything compiled at `-O0`). When such a function is missing, Enzyme reports that
+everything clang compiles at `-O0`; flang does not mark them). When such a function is missing, Enzyme reports that
 it has no derivative for it; compile it in the same file as the call, raise the limit
 with `-Wl,-mllvm,-import-instr-limit=<N>`, or use full `-flto`.
 

enzyme/test/Fortran/ReverseMode/config_file_lto.f90

diff --git a/enzyme/test/Fortran/ReverseMode/config_file_lto.f90 b/enzyme/test/Fortran/ReverseMode/config_file_lto.f90
index 4de620a..022a843 100644
--- a/enzyme/test/Fortran/ReverseMode/config_file_lto.f90
+++ b/enzyme/test/Fortran/ReverseMode/config_file_lto.f90
@@ -12,11 +12,10 @@
 ! RUN: %fc -cpp -DCALLEE_ONLY -flto=thin -O2 -c %flangEnzymeConfig %s -o %t.callee.thin.o
 ! RUN: %fc -cpp -DCALLER_ONLY -flto=thin -O2 -c %flangEnzymeConfig %s -o %t.caller.thin.o
 ! RUN: %fc -flto=thin -O2 %flangEnzymeConfig %t.caller.thin.o %t.callee.thin.o -o %t2 && %t2 | FileCheck %s
-! At -O0 the pre-link run defers as well (LLVM 24 and later). Every function
-! compiled at -O0 is noinline, which ThinLTO only imports with -force-import-all.
+! At -O0 the pre-link run defers as well (LLVM 24 and later).
 ! RUN: if [ %llvmver -ge 24 ]; then %fc -cpp -DCALLEE_ONLY -flto=thin -O0 -c %flangEnzymeConfig %s -o %t.callee.thin0.o; fi
 ! RUN: if [ %llvmver -ge 24 ]; then %fc -cpp -DCALLER_ONLY -flto=thin -O0 -c %flangEnzymeConfig %s -o %t.caller.thin0.o; fi
-! RUN: if [ %llvmver -ge 24 ]; then %fc -flto=thin -O2 %flangEnzymeConfig -Wl,-mllvm,-force-import-all %t.caller.thin0.o %t.callee.thin0.o -o %t3 && %t3 | FileCheck %s; fi
+! RUN: if [ %llvmver -ge 24 ]; then %fc -flto=thin -O2 %flangEnzymeConfig %t.caller.thin0.o %t.callee.thin0.o -o %t3 && %t3 | FileCheck %s; fi
 
 #ifndef CALLER_ONLY
 real function cube(x)