- use default compiler (fortran, C, C++) for OpenBSD
- prefer -O2 as default optimization flag

Index: src/fpm_compiler.f90
--- src/fpm_compiler.f90.orig
+++ src/fpm_compiler.f90
@@ -51,6 +51,7 @@ enum, bind(C)
     enumerator :: &
         id_unknown, &
         id_gcc, &
+        id_cc_openbsd, &
         id_f95, &
         id_caf, &
         id_intel_classic_nix, &
@@ -135,6 +136,7 @@ character(*), parameter :: &
     flag_gnu_coarray = " -fcoarray=single", &
     flag_gnu_backtrace = " -fbacktrace", &
     flag_gnu_opt = " -O3 -funroll-loops", &
+    flag_openbsd_opt = " -O2 -funroll-loops", &
     flag_gnu_debug = " -g", &
     flag_gnu_pic = " -fPIC", &
     flag_gnu_warn = " -Wall -Wextra -Wimplicit-interface", &
@@ -227,6 +229,14 @@ subroutine get_release_compile_flags(id, flags)
             flag_gnu_limit//&
             flag_gnu_coarray
 
+    case(id_cc_openbsd)
+        flags = &
+            flag_openbsd_opt//&
+            flag_gnu_external//&
+            flag_gnu_pic//&
+            flag_gnu_limit//&
+            flag_gnu_coarray
+
     case(id_f95)
         flags = &
             flag_gnu_opt//&
@@ -315,7 +325,7 @@ subroutine get_debug_compile_flags(id, flags)
             flag_gnu_debug//&
             flag_gnu_check//&
             flag_gnu_backtrace
-    case(id_gcc)
+    case(id_gcc, id_cc_openbsd)
         flags = &
             flag_gnu_warn//&
             flag_gnu_pic//&
@@ -403,7 +413,7 @@ pure subroutine set_cpp_preprocessor_flags(id, flags)
     select case(id)
     case default
         flag_cpp_preprocessor = ""
-    case(id_caf, id_gcc, id_f95, id_nvhpc)
+    case(id_caf, id_gcc, id_cc_openbsd, id_f95, id_nvhpc)
         flag_cpp_preprocessor = "-cpp"
     case(id_intel_classic_windows, id_intel_llvm_windows)
         flag_cpp_preprocessor = "/fpp"
@@ -500,7 +510,7 @@ function get_include_flag(self, path) result(flags)
         & id_flang, id_flang_new, id_f18, &
         & id_intel_classic_nix, id_intel_classic_mac, &
         & id_intel_llvm_nix, id_lahey, id_nag, id_ibmxl, &
-        & id_lfortran)
+        & id_lfortran, id_cc_openbsd)
         flags = "-I "//path
 
     case(id_intel_classic_windows, id_intel_llvm_windows)
@@ -518,7 +528,7 @@ function get_module_flag(self, path) result(flags)
     case default
         flags = "-module "//path
 
-    case(id_caf, id_gcc, id_f95, id_cray, id_lfortran)
+    case(id_caf, id_gcc, id_f95, id_cray, id_lfortran, id_cc_openbsd)
         flags = "-J "//path
 
     case(id_nvhpc, id_pgi, id_flang)
@@ -569,7 +579,7 @@ subroutine get_default_c_compiler(f_compiler, c_compil
     case(id_ibmxl)
         c_compiler='xlc'
 
-    case(id_lfortran)
+    case(id_lfortran, id_cc_openbsd)
         c_compiler = 'cc'
 
     case(id_gcc)
@@ -607,6 +617,9 @@ subroutine get_default_cxx_compiler(f_compiler, cxx_co
     case(id_lfortran)
         cxx_compiler = 'cc'
 
+    case(id_cc_openbsd)
+        cxx_compiler = 'c++'
+
     case(id_gcc)
         cxx_compiler = 'g++'
 
@@ -659,8 +672,13 @@ function get_id(compiler) result(id)
 
     integer :: stat
 
-    if (check_compiler(compiler, "gfortran")) then
-        id = id_gcc
+    if (check_compiler(compiler, "gfortran") .or. check_compiler(compiler, "egfortran")) then
+        select case (get_os_type())
+        case default
+            id = id_gcc
+        case(OS_OPENBSD)
+            id = id_cc_openbsd
+        end select
         return
     end if