Fix compilation errors with libc++ on QNX 7

This patch fixes the compilation errors on QNX 7:
1) QNX 7 compiler (i.e qcc based GCC 5.4.0 with libc++ from LLVM) has a
limited c++11 feature support and causing the compilation
errors with the inheriting constructors. This fixes the issues by
providing the required constructors explicitly.

2) Resolves an ambiguous overload error with optional<T>

1 files changed, 6 insertions, 6 deletions

diff --git a/src/mbgl/style/expression/interpolate.cpp b/src/mbgl/style/expression/interpolate.cpp
index 852042382c..54fbc6e1d7 100644
--- a/src/mbgl/style/expression/interpolate.cpp
+++ b/src/mbgl/style/expression/interpolate.cpp
@@ -170,23 +170,23 @@ ParseResult parseInterpolate(const Convertible& value, ParsingContext& ctx) {
             labelValue->match(
                 [&](uint64_t n) {
                     if (n > std::numeric_limits<double>::max()) {
-                        label = {std::numeric_limits<double>::infinity()};
+                        label = optional<double>{std::numeric_limits<double>::infinity()};
                     } else {
-                        label = {static_cast<double>(n)};
+                        label = optional<double>{static_cast<double>(n)};
                     }
                 },
                 [&](int64_t n) {
                     if (n > std::numeric_limits<double>::max()) {
-                        label = {std::numeric_limits<double>::infinity()};
+                        label = optional<double>{std::numeric_limits<double>::infinity()};
                     } else {
-                        label = {static_cast<double>(n)};
+                        label = optional<double>{static_cast<double>(n)};
                     }
                 },
                 [&](double n) {
                     if (n > std::numeric_limits<double>::max()) {
-                        label = {std::numeric_limits<double>::infinity()};
+                        label = optional<double>{std::numeric_limits<double>::infinity()};
                     } else {
-                        label = {static_cast<double>(n)};
+                        label = optional<double>{n};
                     }
                 },
                 [&](const auto&) {}