*: remove "pure" and "const" attributes from throwing functions

The "pure" and "const" attributes are not so well-defined, and a
recent clang version implements an optimization which pushes the
definition's boundary beyond what I believed it was.  clang now
assumes that functions declared "pure" cannot throw exceptions, even
if they lack the "noexcept" specification.

When compiled with this new clang version, MPD will crash randomly if
an exception happens to get thrown by such as "pure" function
(https://github.com/MusicPlayerDaemon/MPD/issues/41).

This commit removes all such misplaced "pure" and "const" attributes,
closing #41.

src/config/Block.cxx

@@ -129,7 +129,6 @@ ConfigBlock::GetBlockValue(const char *name, unsigned default_value) const
 	return bp->GetUnsignedValue();
 }
 
-gcc_pure
 bool
 ConfigBlock::GetBlockValue(const char *name, bool default_value) const
 {

src/config/Block.hxx

@@ -44,13 +44,10 @@ struct BlockParam {
 	BlockParam(const char *_name, const char *_value, int _line=-1)
 		:name(_name), value(_value), line(_line), used(false) {}
 
-	gcc_pure
 	int GetIntValue() const;
 
-	gcc_pure
 	unsigned GetUnsignedValue() const;
 
-	gcc_pure
 	bool GetBoolValue() const;
 };
 
@@ -116,13 +113,10 @@ struct ConfigBlock {
 	AllocatedPath GetPath(const char *name,
 			      const char *default_value=nullptr) const;
 
-	gcc_pure
 	int GetBlockValue(const char *name, int default_value) const;
 
-	gcc_pure
 	unsigned GetBlockValue(const char *name, unsigned default_value) const;
 
-	gcc_pure
 	bool GetBlockValue(const char *name, bool default_value) const;
 };
 

src/config/ConfigGlobal.hxx

@@ -61,18 +61,9 @@ config_get_block(enum ConfigBlockOption option) noexcept;
  * @param key the attribute name
  * @param value the expected attribute value
  */
-gcc_pure
 const ConfigBlock *
 config_find_block(ConfigBlockOption option, const char *key, const char *value);
 
-/* Note on gcc_pure: Some of the functions declared pure are not
-   really pure in strict sense.  They have side effect such that they
-   validate parameter's value and signal an error if it's invalid.
-   However, if the argument was already validated or we don't care
-   about the argument at all, this may be ignored so in the end, we
-   should be fine with calling those functions pure.  */
-
-gcc_pure
 const char *
 config_get_string(enum ConfigOption option,
 		  const char *default_value=nullptr) noexcept;
@@ -87,11 +78,9 @@ config_get_string(enum ConfigOption option,
 AllocatedPath
 config_get_path(enum ConfigOption option);
 
-gcc_pure
 unsigned
 config_get_unsigned(enum ConfigOption option, unsigned default_value);
 
-gcc_pure
 static inline std::chrono::steady_clock::duration
 config_get_unsigned(ConfigOption option,
 		    std::chrono::steady_clock::duration default_value)
@@ -101,11 +90,9 @@ config_get_unsigned(ConfigOption option,
 	return std::chrono::steady_clock::duration(u);
 }
 
-gcc_pure
 unsigned
 config_get_positive(enum ConfigOption option, unsigned default_value);
 
-gcc_pure
 static inline std::chrono::steady_clock::duration
 config_get_positive(ConfigOption option,
 		    std::chrono::steady_clock::duration default_value)
@@ -115,7 +102,6 @@ config_get_positive(ConfigOption option,
 	return std::chrono::steady_clock::duration(u);
 }
 
-gcc_pure
 bool config_get_bool(enum ConfigOption option, bool default_value);
 
 #endif

src/config/Param.hxx

@@ -71,7 +71,6 @@ struct ConfigParam {
 	 *
 	 * Throws #std::runtime_error on error.
 	 */
-	gcc_pure
 	AllocatedPath GetPath() const;
 };