llvm: Remove BPF from targets

To use clang with BPF for v4l-utils, libbpf must be installed but it's
not a BLFS package.  And I doubt if any BLFS user really uses an IR
remote control on the BLFS system.  So let's not make all BLFS users
build something useless.

Note that if both clang and libbpf both exist, v4l-utils will attempt to
use "clang -target bpf" anyway even if -Dbpf=disabled is explicitly
specified (we've got enough surprise from v4l-utils building system
these days!!), so add a note to v4l-utils for people installing non-BLFS
libbpf.

general/prog/llvm.xml

@@ -310,18 +310,18 @@ sed '/^set(LLVM_COMMON_CMAKE_UTILS/d'                   \
 <screen><userinput>mkdir -v build &amp;&amp;
 cd       build &amp;&amp;
 
-CC=gcc CXX=g++                                  \
-cmake -DCMAKE_INSTALL_PREFIX=/usr               \
-      -DLLVM_ENABLE_FFI=ON                      \
-      -DCMAKE_BUILD_TYPE=Release                \
-      -DLLVM_BUILD_LLVM_DYLIB=ON                \
-      -DLLVM_LINK_LLVM_DYLIB=ON                 \
-      -DLLVM_ENABLE_RTTI=ON                     \
-      -DLLVM_TARGETS_TO_BUILD="host;AMDGPU;BPF" \
-      -DLLVM_BINUTILS_INCDIR=/usr/include       \
-      -DLLVM_INCLUDE_BENCHMARKS=OFF             \
-      -DCLANG_DEFAULT_PIE_ON_LINUX=ON           \
-      -Wno-dev -G Ninja ..                      &amp;&amp;
+CC=gcc CXX=g++                              \
+cmake -DCMAKE_INSTALL_PREFIX=/usr           \
+      -DLLVM_ENABLE_FFI=ON                  \
+      -DCMAKE_BUILD_TYPE=Release            \
+      -DLLVM_BUILD_LLVM_DYLIB=ON            \
+      -DLLVM_LINK_LLVM_DYLIB=ON             \
+      -DLLVM_ENABLE_RTTI=ON                 \
+      -DLLVM_TARGETS_TO_BUILD="host;AMDGPU" \
+      -DLLVM_BINUTILS_INCDIR=/usr/include   \
+      -DLLVM_INCLUDE_BENCHMARKS=OFF         \
+      -DCLANG_DEFAULT_PIE_ON_LINUX=ON       \
+      -Wno-dev -G Ninja ..                  &amp;&amp;
 ninja</userinput></screen>
 
     <para>
@@ -465,10 +465,10 @@ rmdir -v --ignore-fail-on-non-empty /usr/share/doc/LLVM</userinput></screen>
     </para>
 
     <para>
-      <parameter>-DLLVM_TARGETS_TO_BUILD="host;AMDGPU;BPF"</parameter>: This
+      <parameter>-DLLVM_TARGETS_TO_BUILD="host;AMDGPU"</parameter>: This
       switch enables building for the same target as the host, and also for
-      the r600 AMD GPU used by the Mesa r600 and radeonsi drivers. The BPF
-      target is required to build <xref linkend="v4l-utils"/>. The Default is
+      the r600 AMD GPU used by the Mesa r600 and radeonsi drivers.
+      The default is
       all of the targets. You can use a semicolon separated list. Valid targets
       are: host, X86, Sparc, PowerPC, ARM, AArch64, Mips, Hexagon, Xcore,
       M68K, MSP430, NVPTX, SystemZ, AMDGPU, BPF, CppBackend, or all.

multimedia/libdriv/v4l-utils.xml

@@ -101,6 +101,19 @@
   <sect2 role="installation">
     <title>Installation of v4l-utils</title>
 
+    <note>
+      <para>
+        If you've installed both LLVM and libbpf (not in BLFS), either
+        enable the BPF target (via
+        <option>-DLLVM_TARGETS_TO_BUILD=</option>) building LLVM, or disable
+        the infrared remote control decoders based on BPF:
+      </para>
+
+      <!-- not "nodump" because it's harmless for BLFS anyway -->
+      <screen><userinput>sed '/^ir_bpf_enabled/s/=.*/= false/' \
+    -i utils/keytable/meson.build</userinput></screen>
+    </note>
+
     <para>
       Install <application>v4l-utils</application> by running
       the following commands: