[macOS] add room in the binary header for the @rpath entries

Author: perazz

src/fpm_compiler.F90

@@ -107,6 +107,8 @@ module fpm_compiler
     procedure :: get_export_flags    
     !> Get library install name flags
     procedure :: get_install_name_flags
+    !> Generate header padding flags for macOS executables
+    procedure :: get_headerpad_flags
     !> Compile a Fortran object
     procedure :: compile_fortran
     !> Compile a C object
@@ -1144,6 +1146,23 @@ function get_install_name_flags(self, target_dir, target_name) result(flags)
 
 end function get_install_name_flags
 
+!>
+!> Generate header padding flags for install_name_tool compatibility on macOS
+!>
+function get_headerpad_flags(self) result(flags)
+    class(compiler_t), intent(in) :: self
+    character(len=:), allocatable :: flags
+
+    if (get_os_type() /= OS_MACOS) then
+        flags = ""
+        return
+    end if
+
+    ! Reserve enough space in the Mach-O header to safely add two install_name or rpath later
+    flags = " -Wl,-headerpad,0x200"
+
+end function get_headerpad_flags
+
 !> Create new compiler instance
 subroutine new_compiler(self, fc, cc, cxx, echo, verbose)
     !> New instance of the compiler

src/fpm_targets.f90

@@ -1181,7 +1181,12 @@ subroutine resolve_target_linking(targets, model, library, error)
                         target%link_flags = model%get_package_libraries_link(target%package_name, &
                                                                             target%link_flags, &
                                                                             error=error, &
-                                                                            exclude_self=.not.has_self_lib)                                                
+                                                                            exclude_self=.not.has_self_lib)   
+                                                                            
+                        
+                        ! On macOS, add room for 2 install_name_tool paths
+                        target%link_flags = target%link_flags // model%compiler%get_headerpad_flags()
+                        
                     end if
 
                     if (allocated(target%link_libraries)) then