Fix build bot failures.

Unfortunately, not all compilers allow using llvm_unreachable
in a constexpr function.

Author: igorkudrin

llvm/include/llvm/BinaryFormat/Dwarf.h

@@ -533,7 +533,7 @@ unsigned LanguageVendor(SourceLanguage L);
 Optional<unsigned> LanguageLowerBound(SourceLanguage L);
 
 /// The size of a reference determined by the DWARF 32/64-bit format.
-constexpr uint8_t getDwarfOffsetByteSize(DwarfFormat Format) {
+inline uint8_t getDwarfOffsetByteSize(DwarfFormat Format) {
   switch (Format) {
   case DwarfFormat::DWARF32:
     return 4;
@@ -569,7 +569,7 @@ struct FormParams {
 };
 
 /// Get the byte size of the unit length field depending on the DWARF format.
-constexpr uint8_t getUnitLengthFieldByteSize(DwarfFormat Format) {
+inline uint8_t getUnitLengthFieldByteSize(DwarfFormat Format) {
   switch (Format) {
   case DwarfFormat::DWARF32:
     return 4;

llvm/lib/DebugInfo/DWARF/DWARFDebugArangeSet.cpp

@@ -62,10 +62,10 @@ Error DWARFDebugArangeSet::extract(DataExtractor data, uint64_t *offset_ptr) {
   constexpr unsigned CommonFieldsLength = 2 + // Version
                                           1 + // Address Size
                                           1;  // Segment Selector Size
-  constexpr unsigned DWARF32HeaderLength =
+  static const unsigned DWARF32HeaderLength =
       dwarf::getUnitLengthFieldByteSize(dwarf::DWARF32) + CommonFieldsLength +
       dwarf::getDwarfOffsetByteSize(dwarf::DWARF32); // Debug Info Offset
-  constexpr unsigned DWARF64HeaderLength =
+  static const unsigned DWARF64HeaderLength =
       dwarf::getUnitLengthFieldByteSize(dwarf::DWARF64) + CommonFieldsLength +
       dwarf::getDwarfOffsetByteSize(dwarf::DWARF64); // Debug Info Offset