[LinkerWrapper][NFC] Rename 'all' to 'generic' for architecture agnostic IR

Summary:
A previous patch introduced `all` as a special architecture. I have
decided I do not like this name and have changed it to `generic`.

Author: jhuber6

clang/docs/ClangLinkerWrapper.rst

@@ -79,6 +79,14 @@ linking is desired, simply do not run the binaries through the
 ``clang-linker-wrapper``. This will simply append the embedded device code so
 that it can be linked later.
 
+Matching
+========
+
+The linker wrapper will link extracted device code that is compatible with each
+other. Generally, this requires that the target triple and architecture match.
+An exception is made when the architecture is listed as ``generic``, which will
+cause it be linked with any other device code with the same target triple.
+
 Example
 =======
 

clang/test/Driver/linker-wrapper.c

@@ -173,7 +173,7 @@ __attribute__((visibility("protected"), used)) int x;
 // AMD-TARGET-ID: clang{{.*}} -o {{.*}}.img --target=amdgcn-amd-amdhsa -mcpu=gfx90a:xnack- -O2 -Wl,--no-undefined {{.*}}.o {{.*}}.o
 
 // RUN: clang-offload-packager -o %t-lib.out \
-// RUN:   --image=file=%t.elf.o,kind=openmp,triple=amdgcn-amd-amdhsa,arch=all
+// RUN:   --image=file=%t.elf.o,kind=openmp,triple=amdgcn-amd-amdhsa,arch=generic
 // RUN: %clang -cc1 %s -triple x86_64-unknown-linux-gnu -emit-obj -o %t.o -fembed-offload-object=%t-lib.out
 // RUN: llvm-ar rcs %t.a %t.o
 // RUN: clang-offload-packager -o %t1.out \

llvm/lib/Object/OffloadBinary.cpp

@@ -356,7 +356,7 @@ bool object::areTargetsCompatible(const OffloadFile::TargetID &LHS,
     return false;
 
   // If the architecture is "all" we assume it is always compatible.
-  if (LHS.second.equals("all") || RHS.second.equals("all"))
+  if (LHS.second.equals("generic") || RHS.second.equals("generic"))
     return true;
 
   // Only The AMDGPU target requires additional checks.