Cherry-pick https://reviews.llvm.org/D99501 to allow -flto=auto

debian/changelog

@@ -4,6 +4,7 @@ llvm-toolchain-snapshot (1:13~++20210218085556+fcdef15d77bd-1~exp1) UNRELEASED;
   * New snapshot release
   * "run-clang-tidy" install it
   * Only enable libomp-13-doc on supported archs
+  * Cherry-pick https://reviews.llvm.org/D99501 to allow -flto=auto
 
   [ John Paul Adrian Glaubitz ]
   * Add upstream patch D98574 to fix clang macro definitions on sparc64

debian/patches/D99501-ignore-lto-auto.diff

@@ -0,0 +1,31 @@
+Index: llvm-toolchain-snapshot_13~++20210330090254+142d522dedbb/clang/include/clang/Driver/Driver.h
+===================================================================
+--- llvm-toolchain-snapshot_13~++20210330090254+142d522dedbb.orig/clang/include/clang/Driver/Driver.h
++++ llvm-toolchain-snapshot_13~++20210330090254+142d522dedbb/clang/include/clang/Driver/Driver.h
+@@ -51,7 +51,8 @@ enum LTOKind {
+   LTOK_None,
+   LTOK_Full,
+   LTOK_Thin,
+-  LTOK_Unknown
++  LTOK_Unknown,
++  LTOK_Ignored
+ };
+ 
+ /// Driver - Encapsulate logic for constructing compilation processes
+Index: llvm-toolchain-snapshot_13~++20210330090254+142d522dedbb/clang/lib/Driver/Driver.cpp
+===================================================================
+--- llvm-toolchain-snapshot_13~++20210330090254+142d522dedbb.orig/clang/lib/Driver/Driver.cpp
++++ llvm-toolchain-snapshot_13~++20210330090254+142d522dedbb/clang/lib/Driver/Driver.cpp
+@@ -610,9 +610,12 @@ void Driver::setLTOMode(const llvm::opt:
+   LTOMode = llvm::StringSwitch<LTOKind>(LTOName)
+                 .Case("full", LTOK_Full)
+                 .Case("thin", LTOK_Thin)
++                .Case("auto", LTOK_Ignored)
++                .Case("jobserver", LTOK_Ignored)
+                 .Default(LTOK_Unknown);
+ 
+   if (LTOMode == LTOK_Unknown) {
++    // FIXME: check if argument is a number, then ignore, or handle it
+     assert(A);
+     Diag(diag::err_drv_unsupported_option_argument) << A->getOption().getName()
+                                                     << A->getValue();

debian/patches/series

@@ -139,3 +139,4 @@ print-lldb-path.patch
 libcxx-armhf-ftbfs.diff
 lld-use-link-atomic-i386.diff
 lower-python-dep.diff
+D99501-ignore-lto-auto.diff