[vcpkg] Fix bootstrap on VS2015 (microsoft#11891)

* Fix boostrap on VS2015 by removing use of C++17 constexpr lambdas.

src/vcpkg/metrics.cpp

@@ -30,6 +30,14 @@ namespace vcpkg::Metrics
  return "";
  }
 
+ struct append_hexits {
+ constexpr static char hex[17] = "0123456789abcdef";
+ void operator()(std::string& res, std::uint8_t bits) const {
+ res.push_back(hex[(bits >> 4) & 0x0F]);
+ res.push_back(hex[(bits >> 0) & 0x0F]);
+ }
+ };
+
  // note: this ignores the bits of these numbers that would be where format and variant go
  static std::string uuid_of_integers(uint64_t top, uint64_t bottom)
  {
@@ -40,11 +48,7 @@ namespace vcpkg::Metrics
  // uuid_field_size in hex characters, not bytes
  constexpr size_t uuid_size = 8 + 1 + 4 + 1 + 4 + 1 + 4 + 1 + 12;
 
- constexpr static char hex[17] = "0123456789abcdef";
- constexpr static auto write_byte = [](std::string& res, std::uint8_t bits) {
- res.push_back(hex[(bits >> 4) & 0x0F]);
- res.push_back(hex[(bits >> 0) & 0x0F]);
- };
+ constexpr static append_hexits write_byte;
 
  // set the version bits to 4
  top &= 0xFFFF'FFFF'FFFF'0FFFULL;